Therapeutic catheter with imaging

ABSTRACT

Ablation systems and methods of the present disclosure include a catheter including one or more image sensors. The one or more image sensors can facilitate, for example, positioning an ablation electrode at a treatment site of an anatomic structure and, additionally or alternatively, can facilitate controlling delivery of therapeutic energy to a treatment site of an anatomic structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Prov. App. No. 62/330,395, filed May 2, 2016, U.S. Prov. App. No.62/357,704, filed Jul. 1, 2016, U.S. Prov. App. No. 62/399,632, filedSep. 26, 2016, U.S. Prov. App. No. 62/399,625, filed Sep. 26, 2016, U.S.Prov. App. No. 62/420,610, filed Nov. 11, 2016, U.S. Prov. App. No.62/424,736, filed Nov. 21, 2016, U.S. Prov. App. No. 62/428,406, filedNov. 30, 2016, U.S. Prov. App. No. 62/434,073, filed Dec. 14, 2016, U.S.Prov. App. No. 62/468,339, filed Mar. 7, 2017, and U.S. Prov. App. No.62/468,873, filed Mar. 8, 2017, with the entire contents of each ofthese applications hereby incorporated herein by reference.

This application is also related to the following commonly-owned U.S.patent applications filed on even date herewith: Attorney Docket NumberAFRA-0001-P01, entitled “CATHETER SENSING AND IRRIGATING”; AttorneyDocket Number AFRA-0009-P01, entitled “LESION FORMATION”; AttorneyDocket Number AFRA-00010-P01, entitled “PULSED RADIOFREQUENCY ABLATION”;and Attorney Docket Number AFRA-0013-P01, entitled “CATHETER INSERTION.”Each of the foregoing applications is hereby incorporated herein byreference in its entirety.

BACKGROUND

Abnormal rhythms generally referred to as arrhythmia can occur in theheart. Cardiac arrhythmias develop when abnormal conduction in themyocardial tissue modifies the typical heartbeat pattern. Radiofrequency (“RF”) catheter ablation can be used to form lesions thatinterrupt the mechanism of abnormal conduction to terminate certainarrhythmias.

SUMMARY

Ablation systems and methods of the present disclosure include acatheter including one or more image sensors. The one or more imagesensors can facilitate, for example, positioning an ablation electrodeat a treatment site of an anatomic structure and, additionally oralternatively, can facilitate controlling delivery of therapeutic energyto a treatment site of an anatomic structure.

According to one aspect, a catheter includes a catheter shaft having aproximal end portion and a distal end portion, an ablation electrodecoupled to the distal end portion of the catheter shaft, and at leastone image sensor (e.g., at least three image sensors). The ablationelectrode has an inner portion and an outer portion opposite the innerportion. The at least one image sensor is spaced from the inner portionof the ablation electrode and disposed within a volume at leastpartially defined by the ablation electrode, and the at least one imagesensor is directed toward the inner portion of the ablation electrode.

In certain implementations, the ablation electrode can include adeformable portion movable in a direction away from the at least oneimage sensor as the deformable portion expands from a compressed stateto an uncompressed state.

In some implementations, the at least one image sensor can be envelopedby the ablation electrode. For example, the ablation electrode can be atleast partially transparent to imaging energy from the at least oneimage sensor such that the ablation electrode reflects less than half ofthe imaging energy directed from the at least one image sensor towardthe ablation electrode. Additionally, or alternatively, the ablationelectrode can define an open area greater than the total surface area ofthe inner portion of the ablation electrode.

In certain implementations, the catheter can further include anirrigation element coupled to the distal end portion of the cathetershaft. The at least one image sensor can be disposed, for example, alongthe irrigation element. Further, or instead, the irrigation element candefine irrigation holes directed toward a respective field of view ofthe at least one image sensor. As an example, the irrigation holesdefined by the irrigation element can be directed toward the respectivefield of view of the at least one image sensor between the irrigationelement and the inner portion of the ablation electrode.

In some implementations, the at least one image sensor includes acamera. The camera can include, for example, a light source directedtoward the inner portion of the ablation electrode. Additionally, oralternatively, the camera can have at least one field of view includinga distal half of the ablation electrode. For example, the ablationelectrode can include a substantially spherical portion, and the cameracan have at least one field of view including an equator of thesubstantially spherical portion. By way of further or alternativeexample, the at least one image sensor can be spaced from the innerportion of the ablation electrode by a distance less than a focal lengthof the at least one image sensor.

In certain implementations, the at least one image sensor includes atleast one ultrasound transducer. For example, the ablation electrode caninclude a plurality of struts, the plurality of struts collectivelydefining a plurality of open cells. The at least one ultrasoundtransducer can have a beam width at least twice as wide as a respectivetransverse dimension of at least some of the struts. The at least oneultrasound transducer can be, for example, radially symmetric.Additionally, or alternatively, the at least one image sensor caninclude an ultrasound transducer array. Further, or instead, the atleast one image sensor can be spaced from the inner portion of theablation electrode by a distance greater than a focal length of the atleast one image sensor.

In some implementations, the at least one image sensor can be directedin a distal direction.

In certain implementations, the catheter can further include a locationsensor fixed relative to the distal end portion of the catheter shaft.The location sensor can include, for example, a magnetic sensor.

According to another aspect, a catheter ablation system includes acatheter and a catheter interface unit in electrical communication withthe catheter. The catheter includes a catheter shaft having a proximalend portion and a distal end portion, an ablation electrode coupled tothe distal end portion of the catheter shaft, the ablation electrodehaving an inner portion and an outer portion opposite the inner portion,and at least one image sensor spaced from the inner portion of theablation electrode and disposed within a volume at least partiallydefined by the ablation electrode, the at least one image sensordirected toward the inner portion of the ablation electrode. Thecatheter interface unit includes one or more processors and anon-transitory, computer readable storage medium having stored thereoncomputer executable instructions for causing the one or more processorsto receive at least one image from the at least one image sensor, basedat least in part on the at least one image, generate a graphicalrepresentation of an anatomic structure, and send the graphicalrepresentation of the anatomic structure to a graphical user interface.

In certain implementations, the computer executable instructions forcausing the one or more processors to generate the graphicalrepresentation of the anatomic structure can further include slicing thegraphical representation of the anatomic structure along a planeextending through the graphical representation of the anatomicstructure.

In some implementations, the graphical representation of the anatomicstructure can be based at least in part on a plurality of images, atleast some of the images in the plurality of images corresponding todifferent locations of the ablation electrode in the anatomic structure.

In certain implementations, the computer executable instructions forcausing the one or more processors to generate the graphicalrepresentation of the anatomic structure can be further based at leastin part on location of the ablation electrode in the anatomic structure.For example, the location of the ablation electrode in the anatomicstructure can be based at least in part on an electric field present inat least a portion of the anatomic structure.

In some implementations, the location of the ablation electrode in theanatomic structure can be based at least in part on a signal from amagnetic sensor fixed relative to the distal end portion of the cathetershaft.

In certain implementations, the computer executable instructions forcausing the one or more processors to generate the graphicalrepresentation of the anatomic structure can include computer executableinstructions for causing the one or more processors to detect a shape ofthe anatomic structure, a shape the ablation electrode, or a combinationthereof.

In some implementations, the computer executable instructions forcausing the one or more processors to generate the graphicalrepresentation of the anatomic structure can include computer executableinstructions for causing the one or more processors to detect ananatomical boundary (e.g., a blood-tissue boundary) based at least inpart on the at least one image.

In certain implementations, the computer executable instructions ofcausing the one or more processor to generate the graphicalrepresentation of the anatomic structure can include computer executableinstructions for causing the one or more processors to determinethickness of the anatomic structure based at least in part on the atleast one image and to display visual indicia of the thickness on thegraphical user interface. For example, the anatomic structure can be acavity of a heart, and the thickness can be the distance betweenendocardial tissue and epicardial tissue.

In some implementations, the computer executable instructions of causingthe one or more processor to generate the graphical representation ofthe anatomic structure can include computer executable instructions forcausing the one or more processors to detect a change in color of tissuein the anatomic structure based at least in part on the at least oneimage and to send to the graphical user interface an indication of thechange in color of tissue in the anatomic structure. For example, thechange in color of tissue in the anatomic structure can be indicative oflesion progress.

According to another aspect, a catheter ablation system can include acatheter and a catheter interface unit in electrical communication withthe catheter. The catheter can include a catheter shaft having aproximal end portion and a distal end portion, an ablation electrodecoupled to the distal end portion of the catheter shaft, the ablationelectrode having an inner portion and an outer portion opposite theinner portion, and at least one image sensor spaced from the innerportion of the ablation electrode and disposed within a volume at leastpartially defined by the ablation electrode, the at least one imagesensor directed toward the inner portion of the ablation electrode. Thecatheter interface unit can include one or more processors and anon-transitory, computer readable storage medium having stored thereoncomputer executable instructions for causing the one or more processorsto receive at least one image from the at least one image sensor, and,based at least in part on the at least one image, determine thickness oftissue of an anatomic structure.

In certain implementations, the computer executable instructions forcausing the one or more processors to determine thickness of tissue ofthe anatomic structure can be further based on a three-dimensionallocalization of the image sensor. For example, the computer executableinstructions for causing the one or more processors to determinethickness of tissue of the anatomic structure can be further based oninformation from one or more previous positions of the image sensor.Additionally, or alternatively, the information from one or moreprevious positions of the image sensor can include one or more imagesassociated with the respective one or more previous positions of theimage sensor. Further or instead, the information from one or moreprevious positions of the image sensor can include one or morethree-dimensional locations associated with the respective one or moreprevious positions of the image sensor.

According to another aspect, a method includes expanding an ablationelectrode from a compressed state to an uncompressed state, an innerportion of the ablation electrode in the uncompressed state envelopingat least one image sensor, positioning an outer portion of the ablationelectrode at a treatment site in an anatomic structure, the outerportion of the ablation electrode opposite the inner portion of theablation electrode, acquiring at least one image of the treatment sitefrom the at least one image sensor, and delivering RF energy to theablation electrode at the treatment site based at least in part on theat least one image of the treatment site.

In certain implementations, expanding the ablation electrode from thecompressed state to the uncompressed state can include moving theablation electrode in a direction away from the at least one imagesensor.

In some implementations, blood can be movable between the at least oneimage sensor and the inner portion of the ablation electrode with theablation electrode in the uncompressed state.

In certain implementations, the method can further include determiningtissue thickness at the treatment site based at least in part on the atleast one image. For example, delivering RF energy to the ablationelectrode can be based on the tissue thickness at the treatment site.

In some implementations, the method can further include detecting ananatomic boundary based on the at least one image of the treatment site.For example, positioning the outer portion of the ablation electrode atthe treatment site can be based at least in part on the detectedanatomic boundary.

In some implementations, acquiring the at least one image of thetreatment site can include acquiring a plurality of images of thetreatment site from respective different locations of the ablationelectrode within the anatomic structure. For example, the method canfurther include determining a location associated with each respectiveimage and forming a graphical representation of an anatomic boundary(e.g., a representation of endocardial tissue of a heart) based on theplurality of images of the treatment site and the location associatedwith each respective image. The graphical representation of the anatomicboundary can include, for example, a representation of tissue thickness.Additionally, or alternatively, determining the location associated witheach respective image can be based on an electric field present in atleast a portion of the anatomic structure. The electric field can be, insome instances, at least partially generated by one or more electrodesexternal to the anatomic structure. Additionally, or alternatively, theelectric field can be at least partially generated by one or moreelectrodes carried by the ablation electrode within the anatomicstructure.

In certain implementations, determining the location associated witheach respective image can include receiving a signal from a locationsensor (e.g., a magnetic sensor) associated with the ablation electrode.For example, the location sensor can be fixed relative to a distal endportion of a catheter shaft coupled to the ablation electrode.

In some implementations, the at least one image sensor can include atleast one camera and acquiring the image of the treatment site from theat least one image sensor can include delivering irrigation fluid to arespective field of view of the least one camera. For example, the atleast one image sensor can be spaced from the inner portion of theablation electrode by a distance less than a focal length of the atleast one image sensor. Additionally, or alternatively, the irrigationfluid can be delivered between the at least one camera and the innerportion of the ablation electrode.

In certain implementations, the at least one image sensor can include atleast one ultrasound transducer. For example, the at least one imagesensor can be spaced from the inner portion of the ablation electrode bya distance greater than a focal length of the at least one image sensor.

In some implementations, delivering RF energy to the ablation electrodecan be based on detection of microbubbles detected by the at least oneimage sensor.

Other aspects, features, and advantages will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an ablation system during anablation treatment.

FIG. 2 is a perspective view of a catheter of the ablation system ofFIG. 1.

FIG. 3 is a perspective view of a distal end portion of the catheter ofthe ablation system of FIG. 1.

FIG. 4 is a cross-sectional perspective view along cross-section A-A ofFIG. 3.

FIG. 5 is a schematic representation of a jet of irrigation fluid movingfrom an irrigation element to an inner portion of an ablation electrodeof the catheter of FIG. 2.

FIG. 6 is a side view of an ablation electrode of the ablation system ofFIG. 1.

FIG. 7 is a perspective view of the ablation electrode of the ablationsystem of FIG. 1.

FIG. 8 is a cross-sectional view, taken along line B-B in FIG. 7, of theablation electrode of the ablation system of FIG. 1.

FIG. 9 is an exemplary graph of force as a function of displacement of adeformable portion of the ablation electrode of the ablation system ofFIG. 1.

FIG. 10 is a perspective view of sensors and the ablation electrode ofthe ablation system of FIG. 1, with the sensors shown mounted to theablation electrode.

FIG. 11 is a perspective view of a sensor of the ablation system of FIG.1.

FIGS. 12A-12C are schematic representations of a method of forming theablation electrode of the ablation system of FIG. 1.

FIGS. 13A-13E are schematic representations of a method of inserting thecatheter of FIG. 2 into a patient.

FIGS. 14A-C are schematic representations of a method of positioning theablation electrode of the ablation system of FIG. 1 at a treatment siteof a patient.

FIGS. 15A-B are schematic representations of a method of irrigating theablation electrode of the ablation system of FIG. 1.

FIG. 16 is a schematic representation of a side view of a helicalirrigation element of a catheter of an ablation system.

FIG. 17 is a side view of an irrigation element of a catheter of anablation system, the irrigation element including a porous membrane.

FIG. 18 is a perspective view of a distal end portion of a catheter ofan ablation system.

FIG. 19 is a perspective view of a distal end portion of a catheter ofan ablation system.

FIG. 20 is a cross-sectional perspective view along cross-section D-D ofFIG. 19.

FIG. 21 is a perspective view of a distal end portion of a catheter ofan ablation system.

FIG. 22 is a cross-sectional side view of the catheter of FIG. 21 alongcross-section E-E. of FIG. 21.

FIG. 23 is a schematic representation of a trajectory around an outersurface of an ablation electrode of the catheter of FIG. 21, thetrajectory used to present simulation results of current densityassociated with the ablation electrode.

FIG. 24 is a graph of percentage change in simulated current densityalong the trajectory shown in FIG. 23, at a fixed distance of 1 mm froman outer surface of the ablation electrode.

FIG. 25 is a graph of depth and width of lesions applied to chickenbreast meat using the ablation electrode of FIG. 21 in axial and lateralorientations relative to the chicken breast meat.

FIG. 26 is a perspective view of a distal portion of a catheter of anablation system, the catheter including an image sensor.

FIG. 27 is a cross-sectional side view of the catheter of FIG. 27 alongthe cross-section F-F of FIG. 26.

FIG. 28 is a flowchart of an exemplary method of displaying a graphicalrepresentation of an anatomic structure.

FIG. 29 is a flowchart of an exemplary method of determining tissuethickness.

FIG. 30 is a flowchart of an exemplary method of delivering therapy to atreatment site.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The present disclosure is generally directed to systems and methods ofablating tissue of a patient during a medical procedure being performedon an anatomic structure of the patient. By way of non-limiting exampleand for the sake of clarity of explanation, the systems and methods ofthe present disclosure are described with respect to ablation of tissuein a heart cavity of the patient as part of an ablation treatmentassociated with the treatment of cardiac arrhythmia. However, it shouldbe appreciated that, unless otherwise specified, the systems and methodsof the present disclosure can be used for any of various differentmedical procedures, such as procedures performed on a hollow anatomicstructure of a patient, in which ablation of tissue is part of a medicaltreatment.

As used herein, the term “physician” should be considered to include anytype of medical personnel who may be performing or assisting a medicalprocedure.

As used herein, the term “patient” should be considered to include anymammal, including a human, upon which a medical procedure is beingperformed.

FIG. 1 is a schematic representation of an ablation system 100 during acardiac ablation treatment being performed on a patient 102. Theablation system 100 includes a catheter 104 connected, via an extensioncable 106, to a catheter interface unit 108. The catheter interface unit108 can be a computing device that includes a processing unit 109 a, anon-transitory, computer readable storage medium 109 b, and a graphicaluser interface 110. The processing unit 109 a can be a controllerincluding one or more processors, and the storage medium 109 b can havestored thereon computer executable instructions for causing the one ormore processors of the processing unit 109 a to carry out one or moreportions of the various methods described herein, unless otherwiseindicated or made clear from the context.

A mapping system 112, a recording system 111, an irrigation pump 114,and a generator 116 can be connected to the catheter interface unit 108.The irrigation pump 114 can be removably and fluidly connected to theablation catheter 104 via fluid line 115. The generator 116 can also, orinstead, be connected, via one or more of wires 117, to one or morereturn electrodes 118 attached to the skin of the patient 102. Therecording system 111 can be used throughout the ablation treatment, aswell as before or after the treatment. The mapping system 112 can beused prior to and/or during an ablation treatment to map the cardiactissue of the patient 102 and determine which region or regions of thecardiac tissue require ablation.

Referring now to FIGS. 2-4, the catheter 104 can include a handle 120, acatheter shaft 122, an ablation electrode 124, sensors 126, and anirrigation element 128. The handle 120 is coupled to a proximal endportion 130 of the catheter shaft 122, and a distal end portion 132 ofthe catheter shaft 122 can be coupled to the irrigation element 128 andto the ablation electrode 124, which supports the sensors 126 in someimplementations. The handle 120 can, further or instead, be coupled tothe fluid line 115 and to one or more of the wires 117 for delivery ofirrigation fluid and electrical energy, respectively, along the cathetershaft 122, to the ablation electrode 124.

As described in further detail below, in a deployed state of theablation electrode 124, irrigation fluid exits irrigation holes 134defined by the irrigation element 128 and is directed toward an innerportion 136 of the ablation electrode 124 while an outer portion 138(opposite the inner portion 136) of the ablation electrode 124 is incontact with tissue as part of an ablation treatment. Spacing betweenthe irrigation holes 134 and the inner portion 136 of the ablationelectrode 124 can facilitate heat transfer between the irrigation fluidand the ablation electrode 124. For example, in the spacing between theirrigation holes 134 and the inner portion 136 of the ablation electrode124, the respective jets of irrigation fluid can develop turbulentcharacteristics. Without wishing to be bound by theory, it is believedthat, as compared to non-turbulent or less turbulent flow of irrigationfluid, increased turbulence can improve local heat transfer from theablation electrode 124 (e.g., from the inner portion 136 of the ablationelectrode 124 to the irrigation fluid). Additionally, or alternatively,blood can flow through the spacing between the irrigation holes 134 andthe inner portion 136 of the ablation electrode 124. As compared toconfigurations in which the flow of blood away from the treatment siteis impeded, the flow of blood through the spacing between the irrigationholes 134 and the inner portion 136 of the ablation electrode 124 can,additionally or alternatively, improve further the local heat transferfrom the outer portion 138 of the ablation electrode 124. In general, itshould be appreciated that such improved local heat transfer can reducethe likelihood of blood clot or charring. As used herein, the term“holes” should be understood to include any size and shape of discreteorifice having a maximum dimension and through which fluid can flow and,thus, should be understood to include any manner and form ofsubstantially geometric shapes (e.g., substantially circular shapes)and, also or instead, substantially irregular shapes, unless otherwisespecified or made clear from the context.

As also described in further detail below, the ablation electrode 124can include a coupling portion 140 and a deformable portion 142. As usedherein, the terms “expandable” and “deformable” are usedinterchangeably, unless otherwise specified or made clear from thecontext. Thus, for example, it should be understood that the deformableportion 142 is expandable unless otherwise specified.

The coupling portion 140 is secured to the distal end portion 132 of thecatheter shaft 122, and the deformable portion 142 can extend distallyfrom the coupling portion 140. The deformable portion 142 of theablation electrode 142 can be deformed for delivery (e.g., through anintroducer sheath, such as an 8F introducer sheath) and expanded at atreatment site to have a cross-sectional dimension larger than across-sectional dimension of the catheter shaft 122. As compared tosmaller ablation electrodes, the ablation electrode 124 can providewider lesions within a shorter period of time, facilitating the creationof a pattern of overlapping lesions (e.g., reducing the likelihood ofarrythmogenic gaps, and reducing the time and number of lesions requiredfor an overlapping pattern, or both). Additionally, or alternatively, alarger tip can facilitate the delivery of more power for providing widerand deeper lesions.

Further, in an expanded state, the deformable portion 142 of theablation electrode 124 is deformable upon sufficient contact force withtissue, and the shape and extent of the deformation can be detectedbased, at least in part, upon signals received from the sensors 126 onthe deformable portion 142 of the ablation electrode 124. As describedin greater detail below, the sensors 126 can be used in one or moremodes of parameter measurement and, for example, can include one or moreof an electrode, a thermistor, an ultrasound transducer, and an opticalfiber. Additionally, or alternatively, the deformable portion 142 can beradiopaque such that deformation of the deformable portion 142 as aresult of contact with tissue is observable, for example, through X-rayor similar visualization techniques. The detection and/or observation ofthe deformation of the deformable portion 142 of the ablation electrode124 can, for example, provide improved certainty that an intendedtreatment is, in fact, being provided to tissue. It should beappreciated that improved certainty of positioning of an ablationelectrode with respect to tissue can reduce the likelihood of gaps in alesion pattern and, also or instead, can reduce the time and number ofablations otherwise required to avoid gaps in a lesion pattern.

The handle 120 can include a housing 145 and an actuation portion 146.In use, the actuation portion 146 can be operated to deflect the distalend portion 132 of the catheter shaft 122 to facilitate positioning theablation electrode 124 into contact with tissue at a treatment site. Thehandle 120 can include a fluid line connector 148 (e.g., a luerconnector) and an electrical connector 149. The fluid line 115 can beconnectable to the fluid line connector 148 and, in use, irrigationfluid (e.g., saline) can be delivered from the irrigation pump 114 tothe catheter 104 where, as described in further detail below, theirrigation fluid is ultimately deliverable through the irrigation holes134 of the irrigation element 128 to the inner portion 136 of theablation electrode 124. The extension cable 106 is connectable to theelectrical connector 149. In use, electrical energy can be deliveredfrom the generator 116 to the catheter 104 where, as described infurther detail below, the electrical energy is ultimately deliverable tothe ablation electrode 124 to ablate tissue in contact with the outerportion 138 of the ablation electrode 124.

The handle 120 can be attached to the proximal end portion 130 of thecatheter shaft 122 through any of various techniques, including one ormore of adhesive bonds, thermal bonds, and mechanical connections.

The catheter shaft 122 defines a lumen 151 extending from the proximalend portion 130 of the catheter shaft 122 to the distal end portion 132of the catheter shaft 122. The lumen 151 can be in fluid communicationwith the irrigation pump 114, via the fluid line 115 and the fluid lineconnector 148 of the handle 120, such that irrigation fluid can bepumped from the irrigation pump 114 to the irrigation holes 134 definedby the irrigation element 128. The catheter shaft 122 can also, orinstead, include electrical wires (such as any one or more of the wires117 shown in FIG. 1) extending along the catheter shaft 122 to carrysignals between the sensors 126 and the catheter interface unit 108 andto carry electrical power from the generator 116 to the ablationelectrode 124.

The catheter shaft 122 can be formed of any of various differentbiocompatible materials that provide the catheter shaft 122 withsufficient sturdiness and flexibility to allow the catheter shaft 122 tobe navigated through blood vessels of a patient. Examples of suitablematerials from which the catheter shaft 122 can be formed includepolyether block amides (e.g., Pebax®, available from Arkema of Colombes,France), nylon, polyurethane, Pellethane® (available from The LubrizolCorporation of Wickliffe, Ohio), and silicone. In certainimplementations, the catheter shaft 122 includes multiple differentmaterials along its length. The materials can, for example, be selectedto provide the catheter shaft 122 with increased flexibility at thedistal end, when compared to the proximal. The catheter shaft 122 canalso, or instead, include a tubular braided element that providestorsional stiffness while maintaining bending flexibility to one or moreregions of the catheter shaft 122. Further, or in the alternative, theshaft material can include radiopaque agents such as barium sulfate orbismuth, to facilitate fluoroscopic visualization.

The catheter shaft 122 can further include pull wires (not shown)mechanically coupled (e.g., via a ring secured to the catheter shaft122) to the distal end portion 132 of the catheter shaft 122 andmechanically coupled to the actuation portion 146 of the handle 120, asis well known in the art. During use, tension may be applied to thewires to deflect the distal end portion 132 of the catheter shaft 122 tosteer the catheter shaft 122 toward a treatment site.

The irrigation element 128 can include a stem 154 and a bulb 156. Thestem 154 can be coupled to the distal end portion 132 of the cathetershaft 122 in fluid communication with the lumen 151 of the cathetershaft 122 and, ultimately, with the irrigation pump 114. The bulb 156defines the irrigation holes 134 and is in fluid communication with thestem 154. Accordingly, irrigation fluid can pass through the lumen 151,through the stem 154, and can exit the irrigation element 128 throughthe irrigation holes 134 defined by the bulb 156.

The stem 154 can be substantially rigid and extend from the distal endportion 132 of the catheter shaft 122 in a direction having a distalcomponent and/or a radial component. For example, a radial extent of thestem 154 can direct irrigation fluid from an off-center position of thelumen 151 to a position along a center axis defined by the cathetershaft 122. Additionally, or alternatively, a distal extent of the stem154 can facilitate clearance of the catheter shaft 122 such that aportion of the irrigation holes 134 directed in the proximal directionhave a substantially unobstructed path to a portion of the inner portion136 of the ablation electrode 124 that is proximal to the irrigationelement 128. Thus, more generally, it should be understood that the sizeand shape of one or more of the stem 154, the bulb 156, and theirrigation holes 134 can be varied to achieve desired directionality ofthe irrigation fluid toward the inner portion 136 of the ablationelectrode 124.

The bulb 156 can be substantially rigid and, in certain implementations,formed of the same material as the stem 154. Additionally, oralternatively, the bulb 156 can be substantially spherical to facilitatedirecting irrigation fluid toward substantially the entire inner portion136 of the ablation electrode 124. It should be appreciated, however,that the bulb 156 can be any of various different shapes that facilitatemulti-directional dispersion of irrigation fluid toward the innerportion 136 of the ablation electrode 124.

In certain implementations, the irrigation holes 134 can be spacedcircumferentially and axially along the irrigation element. For example,the irrigation holes 134 can be spatially distributed along the bulb 156with at least a portion of the irrigation holes 134 arranged to directirrigation fluid in a distal direction with respect to the ablationelectrode 124 and at least a portion of the irrigation holes 134arranged to direct irrigation fluid in a proximal direction with respectto the ablation electrode 124. More generally, the irrigation holes 134can be distributed to produce a relatively uniform dispersion ofirrigation fluid along the inner portion 136 of the ablation electrode124 enveloping the irrigation element 128.

The overall radial extent of the irrigation element 128 can be less thanthe outer diameter of the catheter shaft 122. For example, theirrigation element 128 can remain in the same orientation in a deliveryconfiguration of the catheter 104 to the treatment and during treatmentat the treatment site while, as described in further detail below, theablation electrode 124 expands from a compressed state during deliveryto an expanded state during treatment at the treatment site. As alsodescribed in further detail below, the fixed orientation of theirrigation element 128 can facilitate using the irrigation element 128to act as a sensor or to carry a sensor. For example, a sensor can beadded to the irrigation element 128 to act as a sensor, in cooperationwith the sensors 126 such that the sensor on the irrigation element 128can act as a center electrode and the sensors 126 can act as surfaceelectrodes, as described in greater detail below.

While the irrigation element 128 can extend distal to the catheter shaft122, distal extent of the irrigation element 128 can be limited by theinner portion 136 of the ablation electrode 124. For example, theirrigation element 128 can be spaced relative to the inner portion 136of the ablation electrode 124 such that the irrigation holes 134 directirrigation fluid toward the inner portion 136 of the ablation electrode124 in an expanded state. In particular, given that the deformableportion 142 of the ablation electrode 124 is intended to contact tissueduring ablation, the irrigation holes 134 can be oriented toward thedeformable portion 142 of the ablation electrode 124 to direct fluidtoward the inner portion 136 of the ablation electrode 124 along thedeformable portion 142 in contact with the tissue. Directing theirrigation fluid toward the deformable portion 142 of the ablationelectrode 124 in this way can, for example, reduce the likelihood ofunintended tissue damage resulting from the ablation treatment.

Referring now to FIG. 5, a schematic representation of a jet 158 ofirrigation fluid exiting one of the irrigation holes 134 and movingtoward the inner portion 136 of the ablation electrode 124 is shown justprior to impact between the jet 158 and the inner portion 136. Adistance “L” is a perpendicular distance between the irrigation hole 134and the inner portion 136 of the ablation electrode 124 when theablation electrode 124 is in an undeformed state (e.g., in the absenceof an external force applied to the ablation electrode 124). For thesake of clarity, a two-dimensional cross-section of a single jet isshown. However, it should be understood that, in use, a respectivethree-dimensional jet issues from each of the irrigation holes 134 andthe plurality of jets may interact with one another and/or with thepatient's blood, along the distance “L,” to create additional turbulenceat the inner portion 136 of the ablation electrode 124.

In implementations in which the irrigation holes 134 have a circularcross-section, the ratio of a maximum dimension “D” of each of theirrigation holes 134 to the respective distance “L” between therespective irrigation hole 134 and the inner portion 136 of the ablationelectrode 124 can be greater than about 0.02 and less than about 0.2(e.g., greater than about 0.03 and less than about 0.06). Given otherdesign considerations (e.g., manufacturability of hole sizes of theirrigation holes 134, acceptable pressure drop in the system, theinfluence of blood flow between the irrigation element 128 and theablation electrode 124, or a combination thereof), this range of ratioswill result in turbulent flow of irrigation fluid at the inner portion136 of the ablation electrode 124. Without wishing to be bound bytheory, it is believed that, as compared to configurations with laminarflow and/or less turbulent flow of irrigation fluid past the innerportion 136 of the ablation electrode 124, the turbulent flow ofirrigation fluid moving from the irrigation holes 134 to the innerportion 136 of the ablation electrode 124 results in increased heattransfer, which can reduce unintended tissue damage during ablation.

The size and number of the irrigation holes 134 defined by theirrigation element 128 are selected such that the pressure of irrigationfluid in the irrigation element 128 is sufficient to prevent blood fromentering the irrigation holes 134. For example, providing for somemargin of variation in pressure of the irrigation fluid, the size andnumber of the irrigation holes 134 defined by the irrigation element 128can be selected such that the pressure of the irrigation fluid in theirrigation element 128 is at least about 0.5 psi greater than thepressure of the blood of the patient 102. Further, in implementations inwhich the irrigation element 128 is expandable (e.g., a balloon), thepositive pressure difference between the irrigation fluid within theirrigation element 128 and the blood of the patient 102 can allow theirrigation element 128 to maintain an expanded shape. The size andnumber of the irrigation holes 134 can be, additionally oralternatively, selected to provide substantially uniform coverage of theirrigation fluid on the deformable portion 142 of the ablation electrode124.

In certain implementations, the irrigation holes 134 defined by theirrigation element 128 have a total open area of greater than about 0.05mm² and less than about 0.5 mm². In some implementations, the totalnumber of irrigation holes 134 can be greater than about 50 and lessthan about 250 (e.g., about 200). In implementations in which theirrigation element 128 is substantially rigid (e.g., formed of stainlesssteel and/or platinum iridium), the irrigation holes 134 can be formedinto the irrigation element 128 using any one or more material removaltechniques known in the art, examples of which include drilling and theuse of a laser. In implementations in which the irrigation element 127is formed of an elastomer, the irrigation holes 134 can be formedthrough the use of a laser.

Referring now to FIGS. 1-11, the ablation electrode 124 is a continuousstructure that acts as one electrode in the monopolar electrodeconfiguration of the ablation system 100, shown in FIG. 1. It should beappreciated, however, that the ablation electrode 124 can includeelectrically isolated portions such that the ablation electrode 124includes two electrodes of a bipolar electrode configuration.

The ablation electrode 124 can have an outer diameter of greater thanabout 4 mm and less than about 16 mm (e.g., about 8 mm) and,additionally or alternatively, a thickness of greater than about 0.07 mmand less than about 0.25 mm (e.g., about 0.17 mm). In certainimplementations, the ablation electrode 124 can have greater than about50 percent open area and less than about 95 percent open area (e.g.,about 80 percent open area). As used herein, the percentage of open areaof the ablation electrode 124 should be understood to be the ratio ofthe area through which fluid can flow from the outer portion 138 of theablation electrode 124 to the surface area of a convex hull thatincludes the outer portion 138 of the ablation electrode 124 and thestructural elements defining the outer portion 138 of the ablationelectrode, with the ratio expressed as a percentage. It should beappreciated that the open area of the ablation electrode 124 canfacilitate the flow of irrigation fluid and blood through ablationelectrode 124 during treatment. As compared to ablation electrodes thatimpede the flow of blood, the open area of the ablation electrode 124can reduce the likelihood of local heating of blood at the treatmentsite as ablation energy is delivered to the tissue. It should beappreciated that the delivery of irrigation fluid to the inner portion136 of the ablation electrode 124 can augment the cooling that occursthrough the flow of only blood through the open area.

In general, it should be appreciated that the dimensions of the ablationelectrode 124, including the dimensions related to the diameter,thickness, and/or open area, can facilitate retraction of the ablationelectrode 124. That is, the force required to retract the ablationelectrode 124 into a sheath (e.g., at the end of a procedure) are suchthat the ablation electrode 124 can be retracted by a physician withoutrequiring assistance of a separate mechanism to provide a mechanicaladvantage. Further, or instead, the dimensions of the ablation electrode124 can facilitate adequate expansion of the electrode 124. For example,in instances in which the electrode 124 is formed of nitinol, theablation electrode 124 can be dimensioned such that, in the compressedstate (e.g., for delivery), strain in the ablation electrode 124 is lessthan about ten percent. As a more general example, the ablationelectrode 124 can be dimensioned such that the ablation electrode 124 iscompressible to a size suitable for delivery (e.g., through an 8 Frenchsheath) using a force that avoids, or at least limits, plasticdeformation of the material of the ablation electrode 124. It should beappreciated that avoiding, or at least limiting, plastic deformation inthis way can facilitate expansion of the ablation electrode 124 in apredictable manner (e.g., to a full extent) in the absence of an appliedforce.

The coupling portion 140 of the ablation electrode 124 can be directlyor indirectly mechanically coupled to the catheter shaft 122. Forexample, the coupling portion 140 can include struts 144 a directlycoupled to the catheter shaft 122 or coupled to a transition partcoupled to the catheter shaft 122. Each strut 144 a can include aportion extending parallel to the catheter shaft 122 with the couplingportion 140 coupled to the catheter shaft 122 along the portion of thestrut 144 a extending parallel to the catheter shaft 122. Alternatively,or in addition, the coupling portion 140 can include a complete ringdirectly or indirectly mechanically coupled to the catheter shaft 122.

The coupling portion 140 can be electrically coupled to the generator116 via one or more of the wires 117 (shown in FIG. 1) and/or otherconductive paths extending from the generator 116, along the length ofthe catheter shaft 122, and to the coupling portion 140. For example,the coupling portion 140 can be fitted into the distal end portion 132of the catheter shaft 122, connected to wires extending to the generator116, and potted within an adhesive in the distal end portion 132 of thecatheter shaft 122. In use, electrical energy provided at the generator116 can be delivered to the coupling portion 140 and, thus, to thedeformable portion 142 of the ablation electrode 124, where theelectrical energy can be delivered to tissue of the patient 102.

The deformable portion 142 of the ablation electrode 124 can includestruts 144 b mechanically coupled to one another at joints 141 a todefine collectively a plurality of cells 147 of the ablation electrode124. Additionally, or alternatively, the struts 144 b can bemechanically coupled to one another by a fastener 141 b. Accordingly,each end of the struts 144 b can be coupled to an end of another strut144 b, to the fastener 141 b, or a combination thereof to define thedeformable portion 142 of the ablation electrode 124. For example, thestruts 144 b along the deformable portion 142 of the ablation electrodecan be coupled to one another, to the fastener 141 b, or to acombination thereof to define a closed shape along the deformableportion 142. Also, or instead, at least some of the struts 144 b can becoupled to the struts 144 a to transition between the deformable portion142 and the coupling portion 140 of the ablation electrode 124. Incertain implementations, the struts 144 b can be coupled to the struts144 a such that the coupling portion 140 defines an open shape along thecoupling portion 140 to facilitate, for example, securing the struts 144a to the distal end portion 132 of the catheter shaft 122.

The catheter shaft 122 defines a center axis C_(L)-C_(L) extending fromthe proximal end portion 130 to the distal end portion 132 of thecatheter shaft 122. The cells 147 can have a generally axial orientationrelative to the center axis C_(L)-C_(L). For example, each of the cells147 can have a respective symmetry plane passing through a distal end ofthe cell 147, a proximal end of the cell 147, and the center axisC_(L)-C_(L). Such an orientation can advantageously preferentiallyexpand and contract the cells 147 relative to the center axisC_(L)-C_(L), which can facilitate compressing the deformable portion 142of the ablation electrode 124 to a size suitable for delivery to atreatment site.

The center axis C_(L)-C_(L)can, for example, extend through the fastener141 b in the absence of an external force applied to the ablationelectrode. Such alignment of the fastener 141 b can facilitate, incertain instances, location of the distal end portion 142 of theablation electrode 124 (e.g., by locating the fastener 141 b at atreatment site).

The fastener 141 b can be formed of a first material (e.g., a polymer)and the struts 144 b can be formed of a second material (e.g., anitinol) different from the first material. It should be appreciatedthat the material of the fastener 141 b can be selected for acombination of strength and electrical properties suitable formaintaining the struts 144 b coupled to one another while achieving acurrent density distribution suitable for a particular application. Theclosed shape of the deformable portion 142 can, for example, facilitatethe delivery of substantially uniform current density through theablation electrode 124 in a manner that, as compared to an electrodewith an open shape, is less dependent on the orientation of the ablationelectrode 124 relative to tissue, as described in greater detail below.

In general, each cell 147 can be defined by at least three struts 144 b.Also, or instead, each strut 144 b can define a portion of at least twoof the cells 147. The inner portion 136 of the ablation electrode 124can be in fluid communication with the outer portion 138 of the ablationelectrode 124 through the plurality of cells 147 such that, in use,irrigation fluid, blood, or a combination thereof can move through theplurality of cells 147 to cool the ablation electrode 124 and tissue inthe vicinity of the ablation electrode 124.

At least some of the plurality of cells 147 can be flexible in the axialand lateral directions such that the open framework formed by theplurality of cells 147 along the deformable portion 142 of the ablationelectrode 124 is similarly flexible. For example, at least some of theplurality of cells can be substantially diamond-shaped in theuncompressed state of the deformable portion 142 of the ablationelectrode 124. As used herein, substantially diamond-shaped includesshapes including a first pair of joints substantially aligned along afirst axis and a second pair of joints substantially aligned along asecond axis, different from the first axis (e.g., perpendicular to thefirst axis).

The flexibility of the open framework formed by the plurality of cells147 along the deformable portion 142 of the ablation electrode 124 can,for example, advantageously resist movement of the deformable portion142 in contact with tissue during a medical procedure. That is, thedeformable portion 142 can deform upon contact with tissue and thedeformable portion 142 can engage the tissue through one or more of thecells 147 to resist lateral movement of the deformable portion 142relative to the tissue. That is, as compared to a closed surface incontact with tissue, the deformable portion 142 will resist unintendedmovement (e.g., sliding with respect to the tissue) with which it is incontact. It should be appreciated that such resistance to movement canfacilitate, for example, more accurate placement of lesions.

The struts 144 a, 144 b can have dimensions that differ fromcorresponding dimensions of other ones of the struts 144 a, 144 b. Forexample, the struts 144 b can have a dimension (e.g., width) thatdiffers from a corresponding dimension of another one of the struts 144b. Varying dimensions of the struts 144 a, 144 b, for example, canfacilitate delivery of substantially uniform current density through thedeformable portion 142 of the ablation electrode 124, as described ingreater detail below. Additionally, or alternatively, the struts 144 acan be wider than the struts 144 b to facilitate fixing the struts 144 adirectly or indirectly to the distal end portion 132 of the cathetershaft 122.

In general, the struts 144 b can be dimensioned and arranged relative toone another for delivery of substantially uniform current densitythrough the deformable portion 142 of the ablation electrode 124, asdescribed in greater detail below. By way of non-limiting example, afirst set of the struts 144 b can have a first width, and a second setof the struts 144 b can have a second width, different from the firstwidth. Continuing with this example, the first set of the struts 144 bcan be axially spaced relative to the second set of the struts 144 b.Such axial distribution of the material of the struts can be useful, forexample, for achieving a desired current density profile (e.g., asubstantially uniform current density profile). As another non-limitingexample, at least some of the struts 144 b can have a non-uniform widthalong a length of the respective strut 144 b such that the amount ofmaterial along a given strut is varied, resulting in an associateddistribution in current density. For example, at least some of thestruts 144 b can include a width increasing along the length of therespective strut 144 b in a direction from a proximal region to a distalregion of the ablation electrode 124.

In general, the plurality of cells 147 can be disposed circumferentiallyand axially about the ablation electrode 124. More specifically, asdescribed in greater detail below, the plurality of cells 147 can bearranged about the ablation electrode 124 (e.g., along the deformableportion 142 of the ablation electrode 124) to facilitate contraction andexpansion of the deformable portion 142 and/or to facilitatesubstantially uniform distribution of current density along thedeformable portion 142.

Each cell 147 can be bounded. In particular, as used herein, a boundedcell 147 includes a cell entirely defined by the struts 144 b, thejoints 141 a, sensors 126 disposed along the struts 144 b or the joints141 a, or a combination thereof. As described in further detail below,the struts 144 b can be connected to one another at the joints 141 a aspart of a unitary or substantially unitary structure. Additionally, oralternatively, as also described in greater detail below, the struts 144b can be connected to one another through welds, fasteners, or othermechanical connections at one or more of the joints 141 a.

The struts 144 b can be movable relative to one another through flexingat the joints 141 a. More specifically, the struts 144 b can be flexiblerelative to one another to move the deformable portion 142 between acompressed state, in the presence of an external force, and anuncompressed state, in the absence of the external force. For example, amaximum radial dimension (alternatively referred to herein as a lateraldimension) of the ablation electrode can increase by at least a factorof 2 as the coupled struts 144 b move relative to one another totransition the ablation electrode 124 from a compressed state, in thepresence of external force, to an uncompressed state, in the absence ofexternal force. This ratio of increase in size is achieved through theuse of the open framework of cells 147 formed by the struts 144 b, whichmakes use of less material than would otherwise be required for a solidshape of the same size. Further, or instead, it should be appreciatedthat the ratio of the increase in size achieved through the use of theopen framework of cells 147 is useful for delivery to a treatment sitethrough an 8 French sheath while also facilitating the formation oflarge lesions at the treatment site.

Through flexing at the joints 141 a and associated movement of thestruts 144 b, the deformable portion 142 can be resiliently flexible inan axial direction relative to the catheter shaft 122 and/or in a radialdirection relative to the catheter shaft 122. Additionally, oralternatively, the deformable portion 142 can be expandable (e.g.,self-expandable) from the compressed state to the uncompressed state.For example, the struts 144 b can be biased to move in one or moredirections away from one another to self-expand the deformable portion142 from the compressed state to the uncompressed state. In certaininstances, the inner portion 136 of the ablation electrode 124 along thedeformable portion 142 can be closer in the compressed state than in theuncompressed state to at least a portion of a surface of the irrigationelement 128 and, thus, the inner portion 136 of the ablation electrode124 can move away from at least a portion of the surface of theirrigation element 128 as the deformable portion 142 is expanded fromthe compressed state to the uncompressed state.

In the uncompressed state, the struts 144 b, the joints 141 a, and thecells 147 together can form an open framework having a conductivesurface along the deformable portion 142 of the ablation electrode 124.For example, the open framework formed by the struts 144 b, the joints141 a, and the cells 147 can have greater than about 50 percent openarea along the outer portion 138 of the ablation electrode 124 when thedeformable portion 142 of the ablation electrode 124 is in theuncompressed state. Continuing with this example, in the uncompressedstate, the combined open area of the cells 147 can be greater than thecombined area of the struts 144 b and the joints 141 a along the outerportion 138 of the ablation electrode 124. Further, or instead, at leastsome of the cells 147 can have a larger area in the uncompressed stateof the deformable portion 142 than in the compressed state of thedeformable portion 142.

More generally, the open area defined by the cells 147 can have amagnitude and spatial distribution sufficient to receive the struts 144b and, optionally the sensors 126, as the deformable portion 142collapses from the uncompressed state to the compressed state.Accordingly, it should be appreciated that the magnitude of the ratio ofthe combined open area of the cells 147 to the combined area of thestruts 144 b and the joints 141 a can, among other things, be useful forvarying the degree of expansion of a deformable portion 142 of theablation electrode 124 relative to a delivery state in which thedeformable portion 142 is in a compressed state. That is, the ratio ofthe combined open area of the cells 147 to the combined area of thestruts 144 b and the joints 141 a can facilitate minimally invasivedelivery (e.g., delivery through an 8 Fr sheath) of the ablationelectrode 124.

By way of example, a maximum radial dimension of the ablation electrode124 can increase by at least a factor of 2 as the struts 144 b moverelative to one another to transition the ablation electrode 124 (e.g.,the deformable portion 142 of the ablation electrode 124) from acompressed state, in the presence of an external force (e.g., a radialforce), to an uncompressed state, in the absence of an external force.Additionally, or alternatively, the struts 144 b can be movable relativeto one another such that a maximum radial dimension of the deformableportion 142, in the uncompressed state, is at least about 20 percentgreater than a maximum radial dimension of the catheter shaft 122 (e.g.,greater than a maximum radial dimension of the distal end portion 132 ofthe catheter shaft 122). It should be appreciated that the extension ofthe deformable portion 142 beyond the maximum radial dimension of thecatheter shaft 122 can facilitate creation of a lesion having a largewidth, as compared to an ablation electrode constrained by a radialdimension of a catheter shaft.

In certain implementations, the ablation electrode 124 has a maximumaxial dimension that changes by less than about 33 percent (e.g., about20 percent) as the struts 144 b expand (e.g., self-expand) from theuncompressed state to the compressed state upon removal of an externalradial force applied to the ablation electrode 124.

At least some of the struts 144 b extend in a direction having acircumferential dimensional component with respect to an axis defined bythe catheter shaft 122 (e.g., an axis defined by the proximal endportion 130 and the distal end portion 132 of the catheter shaft 122).That is, the struts 144 b extending in a direction having acircumferential dimensional component with respect to an axis defined bythe catheter shaft 122 are nonparallel to the axis defined by thecatheter shaft 122. In some implementations, at least some of the struts144 b include a non-uniform width along a length of the respective strut144 b. Because current density at a given point along the ablationelectrode 124 is a function of the amount of surface area at the givenpoint along the ablation electrode 124, the non-uniform width of a givenone of the struts 144 b can facilitate balancing current density toachieve a target current density profile along the deformable portion142 of the ablation electrode 124. As described in greater detail below,the circumferential extension and/or the non-uniform width along thelength of at least some of the struts 144 b can facilitate substantiallyuniform distribution of current density along the deformable portion 142during a medical procedure.

While a large surface area of the struts 144 b can be advantageous forthe delivery of energy to tissue, an upper boundary of the area of thestruts 144 b can be the geometric configuration that will allow thestruts 144 b to collapse into the compressed state (e.g., duringdelivery to the treatment site and/or during contact with tissue at thetreatment site) without interfering with one another. Additionally, oralternatively, the struts 144 b can be twisted towards the inner portion136 of the ablation electrode 124. It should be appreciated that, ascompared to struts that are not twisted, the twisted struts 144 b can bewider while still being collapsible into the compressed state withoutinterfering with one another. Further in addition or further in thealternative, an upper boundary of the area of the struts 144 b can bethe amount of open area of the deformable portion 142 that willfacilitate appropriate heat transfer (e.g., during ablation) at theablation electrode 124 through the movement of irrigation fluid and/orblood through the deformable portion 142.

As used herein, the uncompressed state of the deformable portion 142refers to the state of the deformable portion 142 in the absence of asubstantial applied force (e.g., an applied force less than about 5grams). Thus, the uncompressed state of the deformable portion 142includes a state of the ablation electrode 124 in the absence ofexternal forces. Additionally, the uncompressed state of the deformableportion 142 includes a state of the ablation electrode 124 in which asmall applied force (e.g., less an about 5 grams) is present, but isinsufficient to create a significant deformation in the deformableportion 142.

In the uncompressed state of the deformable portion 142, the ablationelectrode 124 can be bulbous. For example, in the uncompressed state,the deformable portion 142 can be a shape having symmetry in a radialdirection and/or an axial direction relative to the catheter shaft 122.For example, in the uncompressed state the deformable portion 142 can bean ellipsoidal shape such as, for example, a substantially sphericalshape (e.g., an arrangement of the struts 144 b, each strut 144 b havinga planar shape, relative to one another to approximate a sphericalshape). Additionally, or alternatively, in the uncompressed state, thedeformable portion 142 can be a symmetric shape (e.g., a substantiallyellipsoidal shape or another similar shape contained between a firstradius and a perpendicular second radius, the first radius and thesecond radius within 30 percent of one another in magnitude). Symmetryof the deformable portion 142 can, for example, facilitate symmetricdelivery of ablation energy to the tissue in a number of orientations ofthe deformable portion 142 relative to the tissue being ablated.

At least when the deformable portion 142 is in the uncompressed state,the deformable portion 142 can envelop the irrigation element 128 suchthat the irrigation element 128 directs irrigation fluid toward theinner portion 136 of the ablation electrode 124. Accordingly, inimplementations in which the deformable portion 142 is symmetric, theirrigation element 128 can provide a substantially uniform distributionof irrigation fluid along the inner portion 136 of the ablationelectrode 124, as the deformable portion 142 in the uncompressed stateenvelops the irrigation element 128.

In certain implementations, the largest cross-sectional dimension of thedeformable portion 142 in the uncompressed state is larger than thelargest cross-sectional dimension of the catheter shaft 122. Thus,because the deformable portion 142 is expandable to extend beyond thecatheter shaft 122, the deformable portion 142 can create a lesion thatis larger than the largest dimension of the catheter shaft 122 such thatthe resulting lesions are wider and deeper than lesions created byablation electrodes that do not expand. For example, in the uncompressedstate, the deformable portion 142 can be substantially circular at thelargest cross-sectional dimension of the deformable portion, and thecatheter shaft 122 can be substantially circular at the largestcross-sectional dimension of the catheter shaft 122. Thus, continuingwith this example, the outer diameter of the deformable portion 142 islarger than the outer diameter of the catheter shaft 122.

The compressed state of the ablation electrode 124, as used herein,refers to the state of the ablation electrode in the presence of a force(e.g., a force of about 5 grams or greater) sufficient to cause thedeformable portion 142 to flex (e.g., through flexing of one or more ofthe joints 141 a) to a significant extent. Thus, for example, thecompressed state of the ablation electrode 124 includes the reduced sizeprofile of the ablation electrode 124 during introduction of thecatheter 104 to the treatment site, as described in further detailbelow. The compressed state of the ablation electrode 124 also includesone or more states of deformation and/or partial deformation resultingfrom an external force exerted along one or more portions of thedeformable portion 142 of the ablation electrode 124 as a result ofcontact between the deformable portion 142 and tissue at the treatmentsite.

The compressed state of the ablation electrode 124 can have apredetermined relationship with respect to an applied force. Forexample, the compressed state of the ablation electrode 124 can have asubstantially linear (e.g., within ±10 percent) relationship withapplied forces in the range of forces typically applied during anablation procedure (e.g., about 1 mm deformation in response to 60 gramsof force). It should be appreciated that such a predeterminedrelationship can be useful, for example, for determining the amount ofapplied force on the ablation electrode 124 based on a measured amountof deformation of the ablation electrode 124. That is, given thepredetermined relationship between deformation of the ablation electrode124 and an amount of an applied force, determining the amount ofdeformation of the ablation electrode 124 can provide an indication ofthe amount of force being applied by the ablation electrode 124 ontissue at the treatment site. As such, the determined amount ofdeformation of the ablation electrode 124 can be used, for example, asfeedback to control the amount of force applied to tissue at thetreatment site. Methods of determining the amount of deformation of theablation electrode 124 are described in greater detail below.

FIG. 9 is a graph of an exemplary relationship between force anddisplacement for different amounts of force applied to the deformableportion 142 of the ablation electrode 124. The deformable portion 142 ofthe ablation electrode 124 can have different force-displacementresponses, depending on the direction of the force applied to thedeformable portion 142 of the ablation electrode 124. For example, asshown in the exemplary relationship in FIG. 9, the deformable portion142 of the ablation electrode 124 can have an axial force-displacementresponse 143 a and a lateral force-displacement response 143 b. That is,the response of the deformable portion 142 to the application of forcecan depend on the direction of the applied force. In the specificexample of FIG. 9, the deformable portion 142 can be stiffer in theaxial direction than in the lateral direction.

In general, the axial force-displacement 143 a and the lateralforce-displacement response 143 b can be reproducible and, thus, theamount of force applied to the deformable portion 142 of the ablationelectrode 124 in the axial and/or lateral direction can be reliablydetermined based on respective displacement of the deformable portion142. Accordingly, as described in greater detail below, the determineddisplacement of the deformable portion 142 can be used to determine theamount and direction of force applied to the deformable portion 142.More generally, because the deformable portion 142 is movable between acompressed state and an uncompressed state in a reproducible manner inresponse to applied force, the deformable portion 142 of the ablationelectrode can be useful as a contact force sensor and, thus, canfacilitate application of appropriate force during ablation treatment.

In certain implementations, at least a portion of the ablation electrode124 is radiopaque, with the deformable portion 142 observable throughthe use of fluoroscopy or other similar visualization techniques. Forexample, the deformable portion 142 of the ablation electrode 124 can beradiopaque such that fluoroscopy can provide an indication of thedeformation and/or partial deformation of the deformable portion 142and, therefore, provide an indication of whether the deformable portion142 is in contact with tissue.

A material for forming the ablation electrode 124 can include nitinol,which is weakly radiopaque and is repeatably and reliably flexiblebetween a compressed state and an uncompressed state. Additionally, oralternatively, the material for forming the ablation electrode 124 canbe coated with one or more of gold or tantalum. Thus, continuing withthis example, the deformable portion 142 of the ablation electrode 124(e.g., the struts 144 b) can be formed of nitinol, either alone orcoated, such that ablation energy is delivered through the nitinolforming the deformable portion 142 for delivery to tissue to createlesions.

As described in further detail below, the deformation and/or partialdeformation of the deformable portion 142 in the compressed state can beadditionally, or alternatively, detected by the sensors 126 to providefeedback regarding the extent and direction of contact between thedeformable portion 142 of the ablation electrode 124 and the tissue atthe treatment site.

Referring now to FIGS. 10 and 11, the sensors 126 can be mounted alongthe deformable portion 142 of the ablation electrode 124. Each sensor126 can be electrically insulated from the ablation electrode 124 andmounted on one of the struts 144 b of the deformable portion 142. Forexample, each sensor 126 can be mounted to the deformable portion 142using a compliant adhesive (e.g., a room temperature vulcanized (RTV)silicone), any of various different mechanical retaining features (e.g.,tabs) between the sensor 126 and the ablation electrode 124, and/ormolding or overmolding of the sensor 126 to the ablation electrode 124.Because the struts 144 b do not undergo significant flexing as thedeformable portion 142 moves between the compressed state and theuncompressed state, mounting the sensors 126 on the struts 144 b canreduce physical strain on the sensors 126, as compared to mounting thesensors 126 on sections of the deformable portion 142 that experiencelarger amounts of flexing as the deformable portion 142 moves betweenthe compressed state and the uncompressed state.

Wires 148 extend from each sensor 126, along the inner portion 136 ofthe ablation electrode 124, and into the catheter shaft 122 (FIG. 2).The wires 148 are in electrical communication with the catheterinterface unit 108 (FIG. 1) such that, as described in further detailbelow, each sensor 126 can send electrical signals to and receiveelectrical signals from the catheter interface unit 108 during use.

In general, the sensors 126 can be positioned along one or both of theinner portion 136 and the outer portion 138 of the ablation electrode124. For example, the sensors 126 can extend through a portion of theablation electrode 124. Such positioning of the sensors through aportion of the ablation electrode 124 can facilitate forming a robustmechanical connection between the sensors 126 and the ablation electrode124. Additionally, or alternatively, positioning the sensors 126 througha portion of the ablation electrode 124 can facilitate measuringconditions along the outer portion 138 and the inner portion 136 of theablation electrode 124.

The sensors 126 can be substantially uniformly spaced from one another(e.g., in a circumferential direction and/or in an axial direction)along the deformable portion 142 of the ablation electrode 124 when thedeformable portion 142 of the ablation electrode 124 is in anuncompressed state. Such substantially uniform distribution of thesensors 126 can, for example, facilitate determining an accuratedeformation and/or temperature profile of the deformable portion 142during use.

Each sensor 126 can act as an electrode (e.g., a surface electrode) todetect electrical activity of the heart in an area local to the sensor126 and, further or instead, each sensor 126 can include a flexibleprinted circuit 150, a thermistor 152 secured between portions of theflexible printed circuit 150, and a termination pad 155 opposite thethermistor 152. As an example, the sensor 126 can be mounted on thedeformable portion 142 of the ablation electrode 124 with the thermistor152 disposed along the outer portion 138 of the deformable portion 142and the termination pad 155 disposed along the inner portion 136 of thedeformable portion 142. In certain instances, the thermistor 152 can bedisposed along the outer portion 138 to provide an accurate indicationof tissue temperature. A thermally conductive adhesive or otherconductive material can be disposed over the thermistor 152 to securethe thermistor 152 to the flexible printed circuit 150.

In some implementations, each sensor 126 can include a radiopaqueportion and/or a radiopaque marker. The addition of radiopacity to thesensor 126 can, for example, facilitate visualization (e.g., usingfluoroscopy) of the sensor 126 during use. Examples of radiopaquematerial that can be added to the sensor 126 include: platinum, platinumiridium, gold, radiopaque ink, and combinations thereof. The radiopaquematerial can be added in any pattern that may facilitate visualizationof the radiopaque material such as, for example, a dot and/or a ring.

In certain implementations, each sensor 126 can form part of anelectrode pair useful for detecting contact between each sensor 126 andtissue. For example, electric energy (e.g., current) can be driventhrough each sensor 126 and another electrode (e.g., any one or more ofthe various different electrodes described herein) and a change in ameasured signal (e.g., voltage or impedance) can be indicative of thepresence of tissue. Because the position of the ablation electrode 124is known, the detection of contact through respective measured signalsat the sensors 126 can be useful for determining a shape of the anatomicstructure in which the ablation electrode 124 is disposed during thecourse of a medical procedure.

In use, each sensor 126 can, further or instead, act as an electrode todetect electrical activity in an area of the heart local to therespective sensor 126, with the detected electrical activity forming abasis for an electrogram associated with the respective sensor 126 and,further or instead, can provide lesion feedback. The sensors 126 can bearranged such that electrical activity detected by each sensor 126 canform the basis of unipolar electrograms and/or bipolar electrograms.Additionally, or alternatively, the sensors 126 can cooperate with acenter electrode (e.g., an electrode associated with an irrigationelement, such as a center electrode 235 in FIGS. 21 and 22 or theirrigation element itself, such as the irrigation element 128 in FIG. 3)to provide near-unipolar electrograms, as described in greater detailbelow. It should be appreciated that the sensors 126 and a centerelectrode can cooperate to provide near-unipolar electrograms inaddition, or as an alternative, to any one or more of the variousdifferent methods of determining contact, shape, force, and impedancedescribed herein, each of which may include further or alternativecooperation between the sensors 126 and a center electrode.

FIGS. 12A-12C are a schematic representation of an exemplary method ofmaking the ablation electrode 124 from a sheet 156 of material.

As shown in FIG. 12A, the sheet 156 of material is flat. As used herein,a flat material includes a material exhibiting flatness within normalmanufacturing tolerances associated with the material. The material ofthe sheet 156 is conductive and, optionally, also radiopaque. Forexample, the sheet 156 can be nitinol.

The thickness of the sheet 156 can correspond to the thickness of theablation electrode 124. For example, the thickness of the sheet 156 canbe greater than about 0.1 mm and less than about 0.20 mm. In certainimplementations, however, the thickness of the sheet 156 can be largerthan at least a portion of the thickness of the ablation electrode 124such that the removal of material from the flat sheet includes removalof material in a thickness direction of the sheet 156. For example,material can be selectively removed in the thickness direction of thesheet 156 to produce the ablation electrode 124 with a variablethickness (e.g., the ablation electrode 124 can be thinner along thejoints 141 a (FIGS. 6-8) to facilitate flexing).

As shown in FIG. 12B, material can be removed from the sheet 156 todefine the open area of the deformable portion 142 and to define thecoupling portion 140. In particular, the removal of material along thedeformable portion 142 can define the struts 144 b and the joints 141 a.

The material of the sheet 156 can be removed, for example, by using anyof various different subtractive manufacturing processes. As an example,the material of the sheet 156 can be removed using chemical etching(also known as photo etching or photochemical etching) according to anyone or more methods that are well known in the art and generally includeremoving material by selectively exposing the material to an acid toremove the material. Additionally, or alternatively, the material of thesheet 156 can be removed by laser cutting the material. The removal ofmaterial can be done to create openings in the sheet 156 and/or to thinselected portions of the sheet 156.

Because the sheet 156 is flat, removing material from the sheet 156 toform the deformable portion 142 can have certain advantages. Forexample, as compared to removing material from a curved workpiece,removing material from the sheet 156 can facilitate controllinggeometric tolerances. Additionally, or alternatively, as compared toremoving material from a curved workpiece, removing material from thesheet 156 can facilitate placement of sensors (e.g., while the sheet 156is flat). In certain implementations, as compared to removing materialfrom a curved workpiece, removing material from the sheet 156 canreduce, or even eliminate, the need to shape set the sheet 156, as thedistal and proximal sections can be put together to form the shape ofthe ablation electrode 124 (e.g., a substantially spherical shape).

In certain implementations, the material removed from the sheet 156 candefine eyelets 157 disposed at one end of at least a portion of thestruts 144 b. The eyelets 157 can be, for example, defined at theintersection of two or more of the struts 144 b.

In general, the material forming the ablation electrode 124 can beprocessed at any of various different stages of fabrication of theablation electrode 124. For example, with the material removed from thesheet to define the struts 144 a, 144 b and the joints 141 a as shown inFIG. 12B, one or more surfaces of the material can be electropolished.Such electropolishing can, for example, be useful for smoothing surfacesand/or otherwise producing fine adjustments in the amount of materialalong the ablation electrode 124.

As shown in FIG. 12C, with the material removed from the sheet 156 todefine the struts 144 a, 144 b and the joints 141 a, the sections 158are bent into proximity with one another and joined to one another toform a unitary three-dimensional structure having the overall shape ofthe ablation electrode 124. For example, the struts 144 b can be benttoward one another and the fastener 141 b can couple the portion of thestruts 144 b to one another at the eyelets 157, thus defining a closeddistal end of the deformable portion 142 of the ablation electrode 124.With the deformable portion 142 defined, the fastener 141 b can be at adistalmost portion of the deformable portion 142.

In certain implementations, the fastener 141 b can be a rivet. In suchimplementations, the eyelets 157 can be, for example, aligned with oneanother such that the fastener 141 b passes through the aligned eyelets157 to hold them together through force exerted on the eyelets 157 bythe fastener 141 b. Additionally, or alternatively, a secondaryoperation such as welding can secure the fastener 141 b to the struts144 b at the eyelets 157.

Referring now to FIGS. 13A-E, to perform a cardiac ablation treatment,the distal end portion 132 of the catheter shaft 122 and, thus, theablation electrode 124 can be first introduced into the patient,typically via a femoral vein or artery. FIGS. 13A-E schematicallyillustrate a series of steps carried out to introduce the ablationelectrode 124 into the patient.

In a first step, shown in FIG. 13A, an introducer sheath 162 ispositioned within a blood vessel of the patient (e.g., the femoralartery of the patient) and the ablation electrode 124 is positioned forinsertion into the introducer sheath 162.

In a second step, shown in FIG. 13B, the user grasps the handle 120 ofthe catheter 104 and distally advances an insertion sheath 164 along thecatheter shaft 122 until the insertion sheath 164 surrounds the ablationelectrode 124. As the insertion sheath 164 is advanced over the ablationelectrode 124, the ablation electrode 124 collapses to a diametercapable of being inserted into the introducer sheath 162.

In a third step, shown in FIG. 13C, the user inserts the insertionsheath 164 (containing the ablation electrode 124) into the introducersheath 162 and distally advances the catheter 104.

In a fourth step, shown in FIG. 13D, after positioning the ablationelectrode 124 within the introducer sheath 162, the ablation electrode124 is advanced out of the insertion sheath 164 that is then leftsurrounding the proximal end portion 130 of the catheter shaft 122throughout the remainder of the treatment.

In a fifth step, shown in FIG. 13E, the catheter 104 is advanced throughthe introducer sheath 162 and the patient's vasculature until theablation electrode 124 reaches the treatment site in the heart of thepatient. As the ablation electrode 124 is extended distally beyond theintroducer sheath 162, the ablation electrode 124 can expand to theuncompressed state.

Because the ablation electrode 124 is collapsible, the introducer sheath162 can have a small diameter that can be inserted through acorrespondingly small insertion site. In general, small insertion sitesare desirable for reducing the likelihood of infection and/or reducingthe amount of time required for healing. In certain implementations, theintroducer sheath 162 can have an 8 French diameter, and the deformableportion 142 (FIG. 3) of the ablation electrode 124 can be collapsible toa size deliverable through the introducer sheath 162 of this size. Insome implementations, the irrigation element 128 is additionallycollapsible to a size smaller than the size of the ablation electrode124 such that the irrigation element 128 and the ablation electrode 124are, together, deliverable through the introducer sheath 162 of thissize.

FIGS. 14A-C schematically represent an exemplary method of positioningthe deformable portion 142 of the ablation electrode 124 into contactwith tissue “T” at the treatment site. It should be appreciated that,because the delivery of ablation energy to the tissue “T” at thetreatment site is enhanced by contact between the ablation electrode 124and the tissue “T,” such contact is established prior to delivery ofablation energy.

In a first step, shown in FIG. 14A, the deformable portion 142 of theablation electrode 124 is away from the tissue “T” and, thus, in anuncompressed state. In certain instances, this uncompressed state isobservable through fluoroscopy. That is, the shape of the deformableportion 142 can be observed in the uncompressed state.

In a second step, shown in FIG. 14B, the deformable portion 142 of theablation electrode 124 makes initial contact with the tissue “T.”Depending on the nature of the contact between the tissue “T” and thedeformable portion 142 of the ablation electrode 124, deformation of thedeformable portion 142 may or may not be observable through fluoroscopyalone. For example, the contact force on the deformable portion 142 maybe insufficient to compress the deformable portion 142 to an extentobservable using fluoroscopy. Additionally, or alternatively, thecontact may not be observable, or may be difficult to observe, in thedirection of observation provided by fluoroscopy.

In a third step, shown in FIG. 14C, the deformable portion 142 of theablation electrode 124 is moved further into contact with the tissue “T”such that sufficient contact is established between the deformableportion 142 and the tissue “T” to deform the deformable portion 142.While such deformation may be observable using fluoroscopy, the degreeand/or direction of the deformation is not readily determined usingfluoroscopy alone. Further, as is also the case with initial contact,the contact and/or degree of contact may not be observable, or may bedifficult to observe, in the direction of observation provided byfluoroscopy. Accordingly, as described in greater detail below,determining apposition of the deformable portion 142 to the tissue “T”can, additionally or alternatively, include sensing the position of thedeformable portion 142 based on signals received from the sensors 126.

Referring again to FIGS. 1 and 3, the sensors 126 can be used todetermine the shape of the deformable portion 142 of the ablationelectrode 124 and, thus, determine whether and to what extent certainregions of the deformable portion 142 are in contact with the tissue“T.” It should be appreciated, however, that the sensing methodsdescribed herein can be carried out using the sensors 126, alone or incombination with another electrode, such as an electrode carried on anirrigation element, as described in greater detail below.

For example, the processing unit 109 a can control the generator 116and/or another electrical power source to drive an electrical signalbetween any number and combination of electrode pairs formed by anycombination of electrodes associated with the ablation electrode 124,and the processing unit 109 a can receive a signal (e.g., a signalindicative of voltage) from another electrode pair or the same electrodepair. For example, the processing unit 109 a can control the generator116 to drive one or more of the sensors 126, the ablation electrode 124,the irrigation element 128, and a center electrode (e.g., a centerelectrode 235 shown in FIGS. 21 and 22). Additionally, or alternatively,multiple pairs can be driven in a multiplexed manner using timedivision, frequency division, code division, or combinations thereof.The processing unit 109 a can also, or instead, receive one or moremeasured electrical signals from one or more of the sensors 126, theablation electrode 124, the irrigation element 128, and a centerelectrode (e.g., the center electrode 235 shown in FIGS. 21 and 22)through which the electrical signal is not being driven. The drivenelectrical signal can be any of various, different forms, including, forexample, a prescribed current or a prescribed voltage. In certainimplementations, the driven electrical signal is an 8 kHz alternatingcurrent applied between one of the sensors 126 and the irrigationelement 128.

In an exemplary method, the impedance detected by an electrode pair canbe detected (e.g., as a signal received by the processing unit 109 a)when an electrical signal is driven through the electrode pair. Theimpedance detected for various electrode pairs can be compared to oneanother and relative distances between the members of each electrodepair determined. For example, if the sensors 126 are identical, eachsensor 126 can be driven as part of a respective electrode pairincluding the irrigation element 128. For each such electrode pair, themeasured impedance between the electrode pair can be indicative ofrelative distance between the particular sensor 126 and the irrigationelement 128 forming the respective electrode pair. In implementations inwhich the irrigation element 128 is stationary while electrical signalsare driven through the electrode pairs, the relative distance betweeneach sensor 126 and the irrigation element 128 can be further indicativeof relative distance between each sensor 126 and each of the othersensors 126. In general, driven electrode pairs with lower measuredimpedance are closer to one another than those driven electrode pairswith higher measured impedance. In certain instances, electrodesassociated with the ablation electrode 124 (e.g., one or more of thesensors 126) that are not being driven can be measured to determineadditional information regarding the position of the driven currentpair.

The measurements received by the processing unit 109 a and associatedwith the driven current pairs alone, or in combination with themeasurements at the sensors 126 that are not being driven, can be fit toa model and/or compared to a look-up table to determine displacement ofthe deformable portion 142 of the ablation electrode 124. For example,the determined displacement of the deformable portion 142 of theablation electrode 124 can include displacement in at least one of anaxial direction or a lateral (radial) direction. It should beappreciated that, because of the spatial separation of the current pairsin three dimensions, the determined displacement of the deformableportion 142 of the ablation electrode 124 can be in more than onedirection (e.g., an axial direction, a lateral direction, andcombinations thereof). Additionally, or alternatively, the determineddisplacement of the deformable portion 142 of the ablation electrode 124can correspond to a three-dimensional shape of the deformable portion142 of the ablation electrode 124.

Based on the determined displacement of the deformable portion 142 ofthe ablation electrode 124, the processing unit 109 a can send anindication of the shape of the deformable portion 142 of the ablationelectrode 124 to the graphical user interface 110. Such an indication ofthe shape of the deformable portion 142 can include, for example, agraphical representation of the shape of the deformable portion 142corresponding to the determined deformation.

In implementations in which the force-displacement response of thedeformable portion 142 is reproducible (e.g., as shown in FIG. 9), theprocessing unit 109 a can determine force applied to the deformableportion 142 based on the determined displacement of the deformableportion 142. For example, using a lookup table, a curve fit, or otherpredetermined relationship, the processing unit 109 a can determine thedirection and magnitude of force applied to the deformable portion 142based on the magnitude and direction of the displacement of thedeformable portion 142, as determined according to any one or more ofthe methods of determining displacement described herein. It should beappreciated, therefore, that the reproducible relationship between forceand displacement along the deformable portion 142, coupled with theability to determine displacement using the sensors 126 disposed alongthe deformable portion 142, can facilitate determining whether anappropriate amount of force is being applied during an ablationtreatment and, additionally or alternatively, can facilitate determiningappropriate energy and cooling dosing for lesion formation.

FIGS. 15A-B schematically represent an exemplary method of cooling theablation electrode 124 at the treatment site with irrigation fluid fromthe irrigation element 128. For the sake of clarity of illustration, asingle jet of irrigation fluid is shown. It should be appreciated,however, that a plurality of jets issue from the irrigation element 128during use. In certain implementations, the irrigation fluid issubstantially uniformly directed to the inner portion 136 of theablation electrode 124. Additionally, or alternatively, a portion of theirrigation fluid can be directed in a direction distal to the irrigationelement 128 and a portion of the irrigation fluid can be directed in adirection proximal to the irrigation element 128.

In a first step, shown in FIG. 15A, the ablation electrode 124 ispositioned at the treatment site with the outer portion 138 disposedtoward tissue. A baseline flow of irrigation fluid is delivered to theirrigation element 128 prior to delivery of ablation energy to theablation electrode 124. The baseline flow of irrigation fluid can be,for example, about 0.5 psi above the patient's blood pressure to reducethe likelihood that blood will enter the irrigation element 128 andclot. Further, as compared to always delivering irrigation fluid at ahigher pressure, the delivery of this lower pressure of irrigation fluidwhen ablation energy is not being delivered to the ablation electrode124 can reduce the amount of irrigation fluid delivered to the patientduring treatment.

In a second step, shown in FIG. 15B, ablation energy is directed to atleast some of the outer portion 138 of the ablation electrode 124 incontact with the tissue “T”. As the ablation energy is delivered to theablation electrode 124, the pressure of the irrigation fluid can beincreased, resulting in a higher pressure flow directed from theirrigation element 128 toward the inner portion 136 of the ablationelectrode 124. The higher flow of irrigation fluid at the inner portion136 can result in turbulent flow which, compared to laminar flow, canimprove heat transfer away from the ablation electrode 124. For example,each jet of irrigation fluid issuing from the irrigation element 128 canhave a Reynolds number above about 2000 (e.g., greater than about 2300)at the inner portion 136 of the ablation electrode 124 when thedeformable portion 142 is in the uncompressed state.

While certain embodiments have been described, other embodiments areadditionally or alternatively possible.

For example, while forming the deformable portion of an ablationelectrode has been described as including removal of material from aflat sheet, other methods of forming a deformable portion of an ablationelectrode are additionally or alternatively possible. For example, adeformable portion of an ablation electrode can be formed by removingmaterial (e.g., by laser cutting) from a tube of material (e.g., a tubeof nitinol). With the material removed, the tube can be bent into asubstantially enclosed shape such as the substantially spherical shapesdescribed herein.

As another example, while the deformable portion of an ablationelectrode has been described as being formed by removing material from aunitary structure of material (e.g., from a plate and/or from a tube),other methods of forming a deformable portion of an ablation electrodeare additionally or alternatively possible. For example, a deformableportion of an ablation electrode can include a mesh and/or a braid. Themesh material can be, for example, nitinol. It should be appreciatedthat this mesh and/or braided portion of the ablation electrode can movebetween a compressed and uncompressed state.

As yet another example, while an ablation electrode has been describedas having a deformable portion, along which sensors are disposed fordetermining displacement of the deformable portion, other configurationsfor determining displacement are additionally or alternatively possible.For example, a plurality of coils can be disposed along a deformableportion of an ablation electrode. In use, some coils in the pluralitycan be used to emit a magnetic field while other coils in the pluralitycan be used to measure the resultant magnetic field. The signalsmeasured can be used to determine displacement of the deformableportion. This determined displacement of the deformable portion can beused, for example, to determine the shape of the deformable portion and,additionally or instead, to determine the force applied to thedeformable portion according to any one or more of the methods describedherein. Further, or instead, a plurality of ultrasound transducers orother types of image sensors can be disposed along a deformable portionof an ablation electrode, on an irrigation element enveloped by thedeformable portion, or a combination thereof. The signals measured bythe ultrasound transducers or other types of image sensors can be usedto determine displacement of the deformable portion.

As still another example, while the deformable portion of an ablationelectrode has been described as being self-expandable from thecompressed state to the uncompressed state, the deformable portion ofthe ablation electrode can be additionally or alternatively expandedand/or contracted through the application of external force. Forexample, a catheter such as any one or more of the catheters describedherein can include a sliding member extending from the handle, though acatheter shaft, and to an ablation electrode. The sliding member can becoupled (e.g., mechanically coupled) to the ablation electrode such thataxial movement of the sliding member relative to the catheter shaft canexert compression and/or expansion force on the deformable portion ofthe ablation electrode. For example, distal movement of the slidingmember can push the ablation electrode in a distal direction relative tothe catheter shaft such that the deformable portion of the ablationelectrode collapses to a compressed state (e.g., for retraction,delivery, or both). In addition, or as an alternative, proximal movementof the sliding member can pull the ablation electrode in a proximaldirection relative to the catheter shaft such that the deformableportion of the ablation electrode expands to an uncompressed state(e.g., for the delivery of treatment). In certain implementations, thesliding member can be mechanically coupled to a portion of the handlesuch that movement of the sliding member can be controlled at thehandle. It should be appreciated that the sliding member can be anelongate member (e.g., a wire) that is sufficiently flexible to bendwith movement of the shaft while being sufficiently rigid to resistbuckling or other types of deformation in response to the force requiredto move the deformable portion of the ablation electrode.

As yet another example, while the irrigation element has been describedas including a substantially rigid stem and bulb configuration, otherconfigurations of the irrigation element are additionally oralternatively possible. For example, referring now to FIG. 16, anirrigation element 128 a can include an axial portion 166 and a helicalportion 168. The irrigation element 128 a can be used in any one or moreof the catheters described herein. For example, the irrigation element128 a can be used in addition to or instead of the irrigation element128, as described with respect to FIGS. 3-5.

The axial portion 166 and the helical portion 168 are in fluidcommunication with one another and, in certain implementations, with anirrigation lumen defined by the catheter shaft. At least the helicalportion 168 and, optionally, the axial portion 166 define a plurality ofirrigation holes 134 a along at least a portion of the length of theirrigation element 128 a. In use, the delivery of irrigation fluidthrough the irrigation holes 134 a can result in an axially,circumferentially, and/or radially distributed pattern. Unless otherwiseindicated or made clear from the context, the irrigation element 128 acan be used in addition to or instead of the irrigation element 128(FIG. 3). Thus, for example, it should be understood that the irrigationelement 128 a can provide substantially uniform cooling along the innerportion 136 of the ablation electrode 124 (FIG. 3).

The irrigation holes 134 a can be similar to the irrigation holes 134defined by the irrigation element 128 (FIG. 3). For example, theirrigation holes 134 a can be the same size and shape as the irrigationholes 134 defined by the irrigation element 128. Additionally, oralternatively, the irrigation holes 134 a can have the same open area asthe irrigation holes 134 defined by the irrigation element 128.

The axial portion 166 of the irrigation element 128 can be coupled to acatheter shaft (e.g., to a distal end portion of the catheter shaft suchas the distal end portion 132 of the catheter shaft 122 described withrespect to FIGS. 2-4). Additionally, or alternatively, the axial portion166 can extend distally from the catheter shaft. For example, the axialportion 166 can extend distally from the catheter shaft, along an axisdefined by the irrigation lumen.

In general, the helical portion 168 extends in a radial direction awayfrom the axial portion 166. In certain implementations, a maximum radialdimension of the helical portion 168 is less than an outer diameter ofthe catheter shaft. In such implementations, the helical portion 168 canremain in the same orientation during delivery and use of the catheter(e.g., during any of the delivery and/or use methods described herein).In some implementations, however, the helical portion 168 can beresiliently flexible (e.g., a nitinol tube shape set in a helicalconfiguration) such that the maximum radial extent of the helicalportion 168 is less than an outer diameter of the catheter shaft duringdelivery to the treatment site and expands such that the maximum radialextent of the helical portion 168 is greater than the outer diameter ofthe catheter shaft in a deployed position. It should be appreciatedthat, in the deployed position, the helical portion can be positionedcloser to the inner surface of an ablation electrode, which canfacilitate delivery of irrigation fluid to the inner surface of theablation electrode.

In addition to extending in a radial direction away from the cathetershaft, the helical portion 168 extends in a circumferential directionrelative to the axial portion 166. For example, the helical portion 168can extend circumferentially about the axial portion 166 through atleast one revolution. Such circumferential extension of the helicalportion through at least one revolution can facilitate substantiallyuniform dispersion of irrigation fluid about an inner surface of asubstantially spherical ablation electrode enveloping the helicalportion 168.

Optionally, the helical portion 168 can further extend in an axialdirection relative to the axial portion 166. Thus, as used herein, thehelical portion 168 should be understood, in the most general sense, toinclude any of various different helical patterns that are substantiallyplanar and/or various different helical patterns that extend axiallyrelative to the axial portion 166.

As another example, while the irrigation element has been described ashaving a discrete number of uniform irrigation holes, otherimplementations are additionally or alternatively possible. For example,referring now to FIG. 17, an irrigation element 128 b can be a porousmembrane defining a plurality of openings 170. In general, the pluralityof openings 170 are a property of the material forming the irrigationelement 128 c and are, therefore, distributed (e.g., non-uniformlydistributed and/or uniformly distributed) along the entire surface ofthe irrigation element 128 b. Because the openings 170 are a property ofthe material forming the irrigation element 128 b, the plurality ofopenings 170 can be substantially smaller than irrigation holes formedin an irrigation element through laser drilling or other similarsecondary processes. Unless otherwise indicated or made clear from thecontext, the irrigation element 128 b can be used in addition to orinstead of the irrigation element 128 (FIG. 3) and/or the irrigationelement 128 a (FIG. 16). Thus, for example, it should be understood thatthe irrigation element 128 b can provide substantially uniform coolingalong the inner portion 136 of the ablation electrode 124 (FIG. 3).

In certain implementations, the irrigation element 128 b can include anarrangement of one or more polymers. Such an arrangement can be porousand/or microporous and, as an example, can be formed ofpolytetrafluoroethylene (PTFE). In such implementations, the openings170 can be defined by spaces between polymeric fibers or through thepolymeric fibers themselves and are generally distributed along theentire surface of the irrigation element 128 b. It should be appreciatedthat the large number of the openings 170 and the distribution of theopenings 170 along the entire surface of the irrigation element 128 bcan produce a substantially uniform spray of irrigation fluid. Further,the large number of the openings 170 and the distribution of theopenings 170 along the entire surface of the irrigation element 128 bcan facilitate interaction of multiple different fluid jets and, thus,the development of turbulent flow of irrigation fluid.

The size and distribution of the openings 170 defined between or throughpolymeric fibers can allow the irrigation element 128 b to act as aselective filter. For example, because blood molecules are substantiallylarger than water molecules, the size (e.g., the average size) of theopenings 170 can be smaller than blood molecules but larger than watermolecules. It should be appreciated that such sizing of the openings 170can permit egress of irrigation fluid from the irrigation element 128 bwhile preventing ingress and, thus, clotting of blood molecules into theirrigation element 128 b.

The arrangement of one or more polymers of the irrigation element 128 bcan include electrospun polytetrafluorethylene and/or expandedpolytetrafluoroethylene (ePTFE). In certain implementations, thearrangement of one or more polymers is nonwoven (as shown in FIG. 17)resulting in the spacing between the fibers being substantiallynon-uniform such that the openings 170 defined by the spacing betweenthe fibers are of non-uniform size and/or non-uniform distribution. Insome implementations, the irrigation element 128 b can include a wovenor fabric arrangement of polymers through which irrigation fluid can bedirected. For example, the fabric can be formed of one or more polymersor other biocompatible materials woven together to form a substantiallyuniform porous barrier through which, in use, irrigation fluid may pass.Examples of polymers that can be arranged together into a fabricsuitable for forming the irrigation element 128 c include, but are notlimited to, one or more of the following: polyester, polypropylene,nylon, PTFE, and ePTFE.

In some implementations, the irrigation element 128 b can include anopen cell foam such that the openings 170 are defined by cells of theopen cell foam along the surface of the irrigation element 128 b. Insuch implementations, irrigation fluid can move through tortuous pathsdefined by the open cell foam until the irrigation fluid reaches theopenings 170 along the surface of the irrigation element 128 b, wherethe irrigation fluid exits the irrigation element 128 b. It should beappreciated that, in such implementations, the openings 170 aredistributed along the entire surface of the irrigation element 128 b,resulting in spray of irrigation fluid issuing from the irrigationelement 128 b in a substantially uniform and substantially turbulentpattern.

As yet another example, while irrigation elements have been described asincluding a resilient, expandable helical portion, other types ofresilient, expandable irrigation elements are additionally oralternatively possible. For example, referring now to FIG. 18, anirrigation element 128 c can be a resilient, inflatable structure, suchas balloon, disposed along a distal end portion 132′ of a catheter shaft122′ and in fluid communication with a lumen 151′. In certainimplementations, the irrigation element 128 c and the ablation electrode124′ can each be coupled to the distal end portion 132′ of the cathetershaft 122′. Unless otherwise indicated or made clear from the context,an element designated with a primed (′) element number in FIG. 18 issimilar to a corresponding element designated with an unprimed number inother figures of the present disclosure and, thus, should be understoodto include the features of the corresponding element designated with anunprimed number. As one example, therefore, the ablation electrode 124′should be understood to correspond to the ablation electrode 124 (FIG.3), unless otherwise specified.

In certain implementations, the irrigation element 128 c is expandable.For example, the irrigation element 128 c can be uninflated and/orunderinflated in a delivery state of the distal end portion 132′ of thecatheter shaft 122′ to a treatment site according to any of the methodsdescribed herein. In such a delivery state, the irrigation element 128 ccan be delivered to the treatment site with a low profile (e.g., aprofile that is less than or equal to a maximum outer dimension of thecatheter shaft 122′). At the treatment site, the irrigation element 128c can be inflated to expand from the delivery state to an expandedstate. For example, the irrigation element 128 c can expand in a radialdirection beyond an outermost dimension of the catheter shaft 122′.

The irrigation element 128 c can be a non-compliant balloon or asemi-compliant balloon. In such implementations, the irrigation element128 c can be substantially resistant to deformation when in an inflatedstate. Thus, in instances in which the irrigation element 128 c isnon-compliant or semi-compliant, the irrigation element 128 c can resistdeformation when contacted by an inner portion 136′ of the deformableportion 142′ of the ablation electrode 124′. As compared to a compliantballoon, this resistance to deformation by the irrigation element 128 ccan facilitate, for example, control over the flow of irrigation fluidthrough the irrigation element 128 c.

In some implementations, the irrigation element 128 c is a balloonformed of one or more polymers. Polymers can be, for example,sufficiently flexible to expand from the delivery state to the expandedstate while withstanding forces created by the movement of irrigationfluid through the irrigation element 128 c. In instances in which theirrigation element 128 c is formed of one or more polymers, irrigationholes can be formed in polymers through laser drilling or other similarsecondary processes. Examples of polymers that can be used to form theirrigation element 128 c include one or more of: thermoplasticpolyurethane, silicone, poly(ethylene terephthalate), and polyetherblock amide.

The irrigation element 128 c can define a plurality of irrigation holes134 c. The irrigation holes 134 c can be similar to the irrigation holes134 defined by the irrigation element 128 (FIG. 3). For example, theirrigation holes 134 c can be the same size and shape as the irrigationholes 134 defined by the irrigation element 128. Additionally, oralternatively, the irrigation holes 134 c can have the same open area asthe irrigation holes 134 defined by the irrigation element 128.

In use, irrigation fluid can flow from the lumen 151′, into theirrigation element 128 c, and can exit the irrigation element 128 cthrough the plurality of irrigation holes 134 c. In general, theplurality of irrigation holes 134 c can have a combined area that isless than the cross-sectional area of the lumen 151′ such that fluidpressure can build in the inflatable element 128 c as the irrigationfluid moves through the irrigation element 128 c. It should beappreciated, then, that the pressure in the inflatable element 128 c,resulting from the flow of irrigation fluid through the irrigationelement 128 c, can inflate the irrigation element 128 c (e.g., from thedelivery state to the expanded state).

In certain implementations, the volume defined by an inner portion 136′of the ablation electrode 124′ in an expanded or uncompressed state islarger than the volume defined by the irrigation element 128 c in anexpanded state. Thus, for example, the inner portion 136′ of theablation electrode 124′ (e.g., along the deformable portion 142′) can bespatially separated from at least a portion of the surface area of theirrigation element 128 c when the irrigation element 128 c is in theexpanded state. This spatial separation can be advantageous, forexample, for developing turbulence of irrigation fluid issuing from theirrigation holes 134 c prior to reaching the inner portion 136′ of theablation electrode 124′. It should be appreciated that, as compared toless turbulent flow and/or laminar flow, such turbulence of the flow ofirrigation fluid at the inner portion 136′ of the ablation electrode124′ can facilitate efficient cooling of the ablation electrode 124′.

The irrigation element 128 c can be enveloped by the ablation electrode124′ in an uncompressed state to facilitate, for example, coolingsubstantially the entire inner portion 136′ of the ablation electrode124′. Additionally, or alternatively, enveloping the irrigation element128 c with the ablation electrode 124′ can reduce the likelihood ofexposing the irrigation element 128 c to undesirable forces such as, forexample, forces that can be encountered as the ablation electrode 124′and the irrigation element 128 c are moved to the treatment site.

In the expanded state, the irrigation element 128 c can include asubstantially ellipsoidal portion. As used herein, a substantiallyellipsoidal portion can include a substantially spherical shape anddeformations of a substantially spherical shape.

In certain implementations, the irrigation holes 134 c are defined onthis ellipsoidal portion of the irrigation element 128 c. Thus, in suchimplementations, the ellipsoidal portion of the irrigation element 128 ccan facilitate directing irrigation fluid in multiple, different axialand radial directions. For example, the irrigation holes 134 c can bespaced circumferentially (e.g., about the entire circumference) aboutthe ellipsoidal portion of the irrigation element 128 c such thatirrigation fluid can be directed toward the inner portion 136′ of theablation electrode 142′ along various different radial directions. As anadditional or alternative example, the irrigation holes 134 c can bespaced axially (e.g., along an entire axial dimension of the ellipsoidalportion of the irrigation element 128 c) such that the irrigation fluidcan be directed toward the inner portion 136′ of the ablation electrode142′ along proximal and/or distal axial directions.

A plurality of sensors 126′ can be supported on the deformable portion142′ of the ablation electrode 124′. In use, the plurality of sensors126′ can be used to detect deformation of the deformable portion 142′.For example, the irrigation element 128 c can include a sensor 172 andelectrical signals can be driven between the one or more electrodes onthe irrigation element 128 c and each of the plurality of sensors 126′according to any of the methods described herein.

While the plurality of sensors 126′ can be used in cooperation with thesensor 172 on the irrigation element 128 c, other configurations forsensing deformation of the deformable portion 142′ are also or insteadpossible. For example, referring now to FIGS. 19 and 20, a plurality ofsensors 174 can be supported along an ablation electrode 124″ at leastpartially enveloping an irrigation element 128 c″. Unless otherwiseindicated or made clear from the context, an element designated with adouble primed (″) element number in FIGS. 19 and 20 is similar to acorresponding element designated with an unprimed number and/or with aprimed number in other figures of the present disclosure and, thus,should be understood to include the features of the correspondingelement designated with an unprimed number and/or with a primed number.As one example, the irrigation element 128 c″ should be understood toinclude the features of the irrigation element 128 c (FIG. 18), unlessotherwise specified or made clear from the context. As another example,the ablation electrode 124″ should be understood to include the featuresof the ablation electrode 124 (FIGS. 3 and 4) and/or of the ablationelectrode 124′ (FIG. 18), unless otherwise specified or made clear fromthe context.

Each sensor 174 can include a flexible printed circuit and/or athermistor similar to any of the flexible printed circuits and/orthermistors described herein, including the flexible printed circuit 150and/or thermistor 152 described above with respect to FIGS. 10 and 11.

In the uncompressed state of the ablation electrode 124″, the innerportion 136″ of the ablation electrode 124″ is spatially separated froma least a portion of a surface of the irrigation element 128 c″ suchthat, for example, at least one of the plurality of sensors 174 is notin contact with the irrigation element 128 c″. In certainimplementations, the ablation electrode 124″ in the uncompressed stateis not in contact with any of the plurality of sensors 174. That is, insuch implementations in which the ablation electrode 124″, in theuncompressed state, is spatially separated from one or more of thesensors 126″, the default arrangement of the sensors 126″ is away fromthe irrigation element 128 c.

The ablation electrode 124″ can include a deformable portion 142″ thatis resiliently flexible from a compressed state (e.g., in which theinner portion 136″ of the ablation electrode 124″ is in contact with theirrigation element 128 c″) to an uncompressed state (e.g., in which theinner portion 136″ of the ablation electrode 124″ is spatially separatedfrom at least a portion of the surface of the irrigation element 128c″). Thus, in such implementations, deformation of the deformableportion 142″ can place one or more of the plurality of sensors 174 intocontact with the irrigation element 128 c″ and sensing this contact canbe used to determine the shape of the deformable portion 142″ inresponse to a deformation force, such as a force exerted through contactwith tissue.

The sensors 174 can be axially and/or circumferentially spaced from oneanother along the deformable portion 142″ of the ablation electrode124″. For example, a first set of the sensors 174 can be disposed distalto a second set of the sensors 174 along the ablation electrode 124″(e.g., along the deformable portion 142″). It should be appreciated thatthe spatial resolution of the detected deformation of the deformableportion 142″ can be a function of the number and spatial distribution ofthe sensors 174, with a larger number of uniformly spaced sensors 174generally providing increased spatial resolution as compared to asmaller number of clustered sensors 174.

In use, an electrical signal can be driven between at least one of thesensors 174 and another one of the sensors 174. Measured electricalsignals generated between at least one of the sensors 174 and another ofthe sensors 174 can be received at a processing unit such as any of theprocessing units described herein (e.g., processing unit 109 a describedwith respect to FIG. 1).

Based at least in part on the measured electrical signals generatedbetween at least one of the sensors 174 and another of the sensors 174,deformation of the deformable portion 142″ of the ablation electrode124″ can be detected. For example, as the deformable portion 142″ of theablation electrode 124″ deforms, one or more of the sensors 174 can bebrought into contact with the irrigation element 128 c″. It should beappreciated that a certain amount of force is required to deform thedeformable portion 142″ by an amount sufficient to bring the one or moresensors 174 into contact with the irrigation element 128 c″. As usedherein, this force can be considered a threshold at least in the sensethat forces below this threshold are insufficient to bring the one ormore sensors 174 into contact with the irrigation element 128 c″ and,therefore, are not detected as contact between the one or more sensors174 and the irrigation element 128 c″.

Contact between the one or more sensors 174 and the irrigation element128 c″ can be detected, for example, as a change in the measuredelectrical signal received, by the processing unit, from the respectiveone or more sensors 174. As a non-limiting example, contact between oneor more of the sensors 174 and the irrigation element 128 c can bedetected as a rise in impedance of a respective one or more electricalsignals associated with the one or more sensors 174 in contact with theirrigation element 128 c.

The detection of deformation of the deformable portion 142″ of theablation electrode 124″ can, for example, include a determination ofwhether one or more of the sensors 174 is in contact with the irrigationelement 128 c. In addition, or instead, the detection of deformation ofthe deformable portion 142″ based on the measured electrical signals caninclude a detection of a degree and/or direction of deformation of thedeformable portion 142″. That is, a degree and/or direction ofdeformation of the deformable portion 142″ can be determined based onthe number and/or position of the one or more sensors 174 detected asbeing in contact with the irrigation element 128 c.

An indication of a determined state of the deformable portion 142″ canbe sent to a graphical user interface, such as any one or more of thegraphical user interfaces described herein (e.g., the graphical userinterface 110 described with respect to FIG. 1). In certainimplementations, the degree and/or orientation of deformation of thedeformable portion 142″ can be sent to the graphical user interface. Forexample, based on which sensors 174 are detected as being in contactwith the irrigation element 128 c, a corresponding representation of thecompressed state of the deformable portion 142″ can be sent to thegraphical user interface. The corresponding representation of thecompressed state of the deformable portion 142″ can be based on, forexample, a look-up table of shapes corresponding to differentcombinations of sensors 174 detected as being in contact with theirrigation element 128 c.

An exemplary method of making a catheter including the irrigationelement 128 c″ can include coupling (e.g., using an adhesive) theirrigation element 128 c″ to a distal end portion 132″ of a cathetershaft 122″. The deformable portion 142″ can be formed according to anyone or more of the methods described herein, and the deformable portion142″ can be positioned relative to the irrigation element 128 c″ suchthat the inner portion 136″ of the ablation electrode 124″ envelops theirrigation element 128 c″. The deformable portion 142″ can be coupled tothe catheter shaft 122″ relative to the irrigation element 128 c″ suchthat, in a compressed state, the inner portion 136″ of the ablationelectrode 124″ is in contact with the irrigation element 128 c″ and, inan uncompressed state, the inner portion 136″ of the ablation electrode124″ along the deformable portion 142″ is spatially separated from theirrigation element 128 c″.

As another example, while certain arrangements of struts to form cellsalong a deformable portion of an ablation electrode have been described,other configurations are additionally or alternatively possible. Forexample, referring now to FIGS. 21 and 22, a catheter 204 can include anablation electrode 224 having struts 244 b defining a plurality of cells247, with the struts 244 b progressively ganged together in a directionfrom a proximal region to a distal region of a deformable portion 242 ofthe ablation electrode 224. For the sake of efficient and cleardescription, elements designated by 200-series element numbers in FIGS.21 and 22 are analogous to or interchangeable with elements with100-series element numbers (including primed and double-primed elementnumbers) described herein, unless otherwise explicitly indicated or madeclear from the context, and, therefore, are not described separatelyfrom counterpart elements having 100-series element numbers, except tonote differences or to describe features that are more easily understoodwith reference to FIGS. 21 and 22. Thus, for example, catheter 204 inFIGS. 21 and 22 should generally be understood to be analogous to thecatheter 104 (FIGS. 1-4), unless otherwise explicitly indicated or madeclear from the context.

As used herein, a progressively ganged together configuration of thestruts 244 b can include an arrangement of the struts 244 b in which thenumber of cells in the plurality of cells 247 decreases in a givendirection. Thus, for example, the struts 244 b can be progressivelyganged together in the direction toward the distal end of the deformableportion 242 such that the number of cells 247 defined by the strutsdecreases in the direction toward the distal end of the deformableportion 242. Thus, as compared to a configuration in which struts areuniformly disposed about a shape, the closed end of the deformableportion 242 of the ablation electrode 224 can be formed by joiningtogether relatively few of the struts 244 b. This can be advantageouswith respect to, for example, achieving acceptable manufacturingtolerances or, further or instead, facilitating substantially uniformdistribution of current density along the deformable portion 242.

In some implementations, the cells in the plurality of cells 247 can bebounded by different numbers of struts 244 b, which can facilitateachieving a target distribution of current density along the deformableportion 242. For example, a first set of cells of the plurality of cells247 can be bounded by struts 244 b defining eyelets (e.g., eyelets 157in FIG. 12B), and a second set of cells of the plurality of cells 247can be bounded by fewer struts than the first set of cells. For example,the first set of cells of the plurality of cells 247 can be bounded byat least four struts 244 b.

In certain implementations, at least some of the cells 247 of theplurality of cells 247 are symmetric. Such symmetry can, for example,facilitate achieving substantially uniform current density in adeformable portion 242 of the ablation electrode 224. Additionally, oralternatively, such symmetry can be useful for achieving suitablecompressibility of the deformable portion for delivery to a treatmentsite (e.g., through a sheath) while also achieving suitable expansion ofthe deformable portion for use at the treatment site.

At least some of the cells 247 can have mirror symmetry. As used herein,a mirror symmetric shape includes a shape that is substantiallysymmetric about a plane intersecting the shape, with the substantialsymmetry allowing for the presence or absence of a sensor 226 on one orboth sides of the plane intersecting the shape. For example, at leastsome of the cells 247 can have mirror symmetry about a respective mirrorsymmetry plane passing through the respective cell 247 and containing acenter axis C_(L)′-C_(L)′ defined by a catheter shaft 222 and extendingfrom a proximal end portion to a distal end portion of the cathetershaft 222. In the side view shown in FIG. 22, a mirror symmetry planefor some of the cells of the plurality of 247 is directedperpendicularly into the page and passes through the center axisC_(L)′-C_(L)′. Additionally, or alternatively, it should be appreciatedthat the overall deformable portion 242 of the ablation electrode 224can be symmetric about a plane including the center axis C_(L)′-C_(L)′,such as the plane directed perpendicularly into the page and passingthrough the center axis C_(L)′-C_(L)′.

The mirror symmetry of at least some of the cells of the plurality ofcells 247 and/or the overall deformable portion 242 can be useful, forexample, for uniform distribution of current density. Additionally, oralternatively, symmetry can facilitate expansion and contraction of thedeformable portion 242 of the ablation electrode 224 in a predictableand repeatable manner (e.g., with little to no plastic deformation). Forexample, each of the cells of the plurality of cells 247 can besymmetric about its respective symmetry plane in the compressed stateand in the uncompressed state of the deformable portion 242 of theablation electrode 224. With such symmetry in the compressed state andin the uncompressed state of the deformable portion 242, the deformableportion 242 can expand with little to no circumferential translation ofthe deformable portion 242 during expansion, which can facilitateaccurate knowledge of the position of the deformable portion 242 duringdelivery and deployment of the deformable portion 242.

The catheter 204 can be formed according to any one or more of thevarious different methods described herein. For example, the ablationelectrode 224 can be formed from a flat sheet or from a tube, asdescribed herein, such that the ablation electrode 224 has two openends. A fastener 241 b can be inserted through an end of at least someof the struts 244 b according to any of the various different methodsdescribed herein to couple ends of the struts 244 b to close one of thetwo open ends of the ablation electrode 224. An open end of ablationelectrode 224 (e.g., an end opposite the fastener 241 b) can be coupledto a distal end portion 232 of the catheter shaft 222 to form thecatheter 204.

The following simulation and experiment describe the uniformity ofcurrent density associated with the ablation electrode 224 in theuncompressed state. It is to be understood that the simulation andexperiment described below are set forth by way of example only, andnothing in the simulation or experiment shall be construed as alimitation on the overall scope of this disclosure.

Referring now to FIG. 23, current density through the deformable portion242 of the ablation electrode 224 (FIG. 21) in the uncompressed statewas simulated using a finite difference method. In the simulation, theablation electrode 224 was assumed to have uniform voltage (e.g., 1 V),with the medium set at uniform resistivity. The return electrode wasassumed to be the edge of the domain and was set to another uniformvoltage (e.g., 0 V). It is believed that the variation in simulatedcurrent density along a trajectory (shown as the arc extending fromposition 0 to position 450) at a fixed distance away from an outersurface of the deformable portion 242 is a proxy for the actualvariation in current density along the respective trajectory of thedeformable portion 242.

Referring now to FIGS. 23 and 24, the simulated current density throughthe deformable portion 242 varies by less than about ±10 percent alongthe trajectory at 1 mm away from an outer surface of the deformableportion 242 in the uncompressed state. Thus, the current density at afixed distance near the deformable portion 242 in the uncompressed stateis believed to be relatively uniform. Thus, more generally, currentdensity near the surface of the deformable portion 242 is substantiallyinsensitive to the orientation of the deformable portion 242 relative totissue. Further, given that the deformable portion 242 in the expandedstate is larger than a maximum lateral dimension of the catheter shaft222 (FIG. 21), the deformable portion 242 can reliably deliver widelesions in any of various different orientations relative to tissue.This can be useful, for example, for reducing treatment time and/orincreasing the likelihood that applied ablation energy is sufficient totreat a targeted arrhythmia.

While the results shown in FIG. 24 are based on a simulation using afinite difference method, the general observations drawn from thesesimulations are supported by the experimental results described below.

FIG. 25 is a graph of depth of lesions applied to chicken breast meatusing the ablation electrode 224 (FIG. 21) in axial and lateralorientations relative to the chicken breast meat. Each lesion wasperformed on chicken breast meat and 0.45% saline solution at bodytemperature and, for each lesion, the deformable portion 242 of theablation electrode 224 (FIG. 21) was in contact with the chicken breastmeat with 10 g of force and 8 mL/min of irrigation was used. For eachablation, 2 amperes were delivered to the tissue through the deformableportion 242 (FIG. 21) for ten seconds. Lesion depth was determined usinga ruler to measure the depth of tissue discolored from pink to white.

Five of the lesions were created with the deformable portion 242 (FIG.21) in an axial orientation in which the catheter shaft 222 (FIG. 21)was perpendicular to the chicken breast, and five of the lesions werecreated with the deformable portion 242 in a lateral orientationperpendicular to the axial orientation. As shown in FIG. 25, althoughthe lesions were created using different orientations, the lesion depthswere similar, with lesion depth varying by less than about ±20 percent,indicating that the amount of energy ablating tissue in bothorientations is similar. This experimental finding is consistent withthe results of the simulation. That is, lesions corresponding tomultiple different angles between the deformable portion 242 (FIG. 21)and tissue have similar depth at each of the multiple different angles.Such uniform distribution of current density can facilitate controllinglesion size, which can be particularly useful for ablating thin tissue.

Referring again to FIGS. 21 and 22, an irrigation element 228 isenveloped by the deformable portion 242 of the ablation electrode 224such that the deformable portion 242 forms an enclosure about theirrigation element 228. The irrigation element 228 can be any of thevarious different irrigation elements described herein and can be influid communication with a catheter shaft 222. For example, theirrigation element 228 can be disposed substantially along the centeraxis C_(L)′-C_(L)′, can extend distally from a distal end portion 232 ofthe catheter shaft 222, and, also or instead, can define a plurality ofirrigation holes 234 disposed along the irrigation element 228 to directirrigation fluid toward the deformable portion 242 of the ablationelectrode 224. Additionally, or alternatively, a center electrode 235can be disposed along the irrigation element 228 and directly orindirectly coupled to the distal end portion 232 of the catheter shaft222.

In the absence of force applied to the deformable portion 242 of theablation electrode 224, the center electrode 235 is spaced apart fromthe sensors 226. As the deformable portion 242 is brought into contactwith tissue through application of force applied to the deformableportion 242, it should be appreciated that, independent of orientationof the deformable portion 242 relative to tissue, the deformable portion242, and thus the sensors 226, makes initial contact with the tissuebefore the center electrode 235 makes initial contact with the tissue.In certain implementations, the center electrode 235 remains spaced fromtissue under normal operation. That is, the deformable portion 242 ofthe ablation electrode 224 can be sufficiently rigid to maintain spacingof the center electrode 235 from tissue under a normal range of contactforces, which are less than about 100 g (e.g., less than about 50 g).

Electrical activity detected (e.g., passively detected) by the centerelectrode 235 and the sensors 226 (acting as surface electrodes) canform the basis of respective electrograms associated with each uniquepairing of the center electrode 235 and the sensors 226. For example, inimplementations in which there are six sensors 226, the center electrode235 can form six electrode pairs with the sensors 226 which, in turn,form the basis for six respective electrograms.

An electrogram formed by electrical signals received from eachrespective electrode pair (i.e., the center electrode 235 and arespective one of the sensors 226) can be generated through any ofvarious different methods. In general, an electrogram associated with arespective electrode pair can be based on a difference between thesignals from the electrodes in the pair and, thus more specifically, canbe based on a difference between an electrical signal received from thecenter electrode 235 and an electrical signal received from a respectiveone of the sensors 226. Such an electrogram can be filtered or otherwisefurther processed to reduce noise and/or to emphasize cardiac electricalactivity, for example.

Because the center electrode 235 remains spaced at an intermediatedistance from the sensors 226 and tissue in the range of forcesexperienced through contact between tissue and the deformable portion242 of the ablation electrode 224, the electrogram formed from eachelectrode pair can advantageously be a near-unipolar electrogram. Asused herein, a near-unipolar electrogram includes an electrogram formedbased on the difference between two electrodes that are greater thanabout 2 mm apart and less than about 6 mm apart and oriented such thatone of the electrodes remains spaced away from tissue. In certainimplementations, in the absence of force applied to the deformableportion 242 of the ablation electrode 224, the center electrode 235 isspaced apart from the sensors 226 by distance greater than about 2 mmand less than about 6 mm.

The near-unipolar electrograms associated with the center electrode 235spaced from the sensors 226 can provide certain advantages over unipolarconfigurations (i.e., configurations having electrode spacing greaterthan 6 mm) and over bipolar configurations (i.e., configurations havingelectrode spacing equal to or less than 2.5 mm and/or allowing bothelectrodes to be spaced close to tissue). For example, as compared tounipolar electrograms, the near-unipolar electrograms formed based onsignals received from the center electrode 235 and the sensors 226 areless noisy and, additionally or alternatively, less susceptible tofar-field interference from electrical activity away from the tissue ofinterest. Also, as compared to unipolar electrograms, a near-unipolarelectrogram does not require a reference electrode on a separatecatheter or other device. As a further or alternative example, ascompared to bipolar electrograms, a near-unipolar electrogram formedbased on signals received from the center electrode 235 and the sensors226 is generated from an electrode pair with only one electrode in theelectrode pair in contact with tissue such that the resultingelectrogram waveform arises from one tissue site, making it less complexto interpret. Also, or instead, as compared to bipolar electrogramsgenerated from a pair of electrodes in contact with tissue, the signalof a near-unipolar electrogram formed based on signals received from thecenter electrode 235 and the sensor 226 in contact with tissue can havea more consistent morphology and/or larger amplitude at least becausethe center electrode 235 is always oriented away from tissue as comparedto the sensor 226 in the electrode pair touching tissue.

The sensors 226 can be any of the various different sensors describedherein and, in addition or in the alternative, can be arranged on thedeformable portion 242 of the ablation electrode 224 according to any ofthe various different arrangements described here. For example, in theabsence of external force applied to the deformable portion 242 of theablation electrode 224 enveloping the center electrode 235, the sensors226 can be noncoplanar relative to one another. It should be appreciatedthat, as compared to a planar arrangement, the electrograms generatedfrom the sensors 226 arranged in such a noncoplanar configuration can beuseful for providing improved directional information regardingelectrical activity in tissue.

The sensors 226 can be electrically isolated from the deformable portion242 of the ablation electrode 224 with the sensors 226, acting assurface electrodes, passively detecting electrical activity in tissue inproximity to each respective sensor 226 without interference from thedeformable portion 242 of the ablation electrode 224. At least some ofthe sensors 226 can be at least partially disposed along an outerportion of the deformable portion 242 of the ablation electrode 224 withthe deformable portion 242 of the ablation electrode between the centerelectrode 235 and at least a portion of each respective one of thesensors 226 along the outer portion. Additionally, or alternatively, atleast some of the sensors 226 can be at least partially disposed alongan inner portion of the deformable portion 242 of the ablation electrode224. In such implementations, each sensor 226 can be in proximity totissue without touching tissue as the deformable portion 242 of theablation electrode 224 touches tissue. Thus, for example, at least someof the sensors 226 can extend through the ablation electrode 224.

Referring now to FIGS. 1, 21, and 22, the catheter 204 can replace thecatheter 104 in FIG. 1. Accordingly, electrical signals from the sensors226 and the center electrode 235 can be directed to the catheterinterface unit 108 and, thus, unless otherwise indicated or made clearfrom the context, should be understood to form a basis for detectingcontact with tissue, detecting deformation of the ablation electrode224, or a combination thereof, according to any one or more of themethods described herein. For example, the signals can be sent to anelectrical input stage associated with the catheter interface unit 108.In certain implementations, the difference between electrical signals isdetermined through electronic circuitry (e.g., a voltage amplifier witha differential input). Additionally, or alternatively, the differencebetween electrical signals can be determined by the processing unit 109a of the catheter interface unit 108.

In general, the storage medium 109 b of the catheter interface unit 108can have stored thereon computer-executable instructions for causing theprocessing unit 109 a to acquire a plurality of electrograms (e.g., anelectrogram for each electrode pair formed by the center electrode 235and each respective sensor 226). The storage medium 109 b be can, alsoor instead, have stored thereon instructions for causing the processingunit 109 a to display a representation of at least one of the pluralityof electrograms on the graphical user interface 110. In certainimplementations, the storage medium 109 b can have stored thereoninstructions for causing the processing unit 109 a to determine avoltage map associated with the plurality of electrograms, the voltagemap corresponding, for example, to electrical activity of a heart of apatient. In some implementations, the storage medium 109 b can havestored thereon instructions for causing the processing unit 109 a todisplay the voltage map on the graphical user interface 110. Thedisplayed electrograms, alone or in combination with a displayed voltagemap, can be useful for selectively treating tissue of the heart (e.g.,delivering ablation energy from the deformable portion 242 of theablation electrode 224 to tissue in a cavity of the heart).

While the center electrode 235 has been described as being disposed onthe irrigation element 228, it should be appreciated that the centerelectrode 235 can additionally or alternatively be located at any ofvarious different positions within the deformable portion 242 of theablation electrode 224. For example, the center electrode 235 can bepositioned on the distal end portion 232 of the catheter shaft 222.Additionally, or alternatively, the irrigation element 228 itself can beused as a center electrode.

As still another example, while catheters have been described asincluding certain sensors, other configurations are additionally oralternatively possible. For example, referring now to FIGS. 26 and 27and as described in greater detail below, a catheter 304 can include ashaft 322, an ablation electrode 324, and at least one image sensor 353.For the sake of efficient and clear description, elements designated by300-series element numbers in FIGS. 26 and 27 are analogous to orinterchangeable with elements with 100-series or 200-series elementnumbers (including primed and double-primed numbers) described herein,unless otherwise explicitly indicated or made clear from the context,and, therefore, are not described separately from counterpart elementshaving 100-series element numbers or 200-series element numbers, exceptto note differences or to described features that are more easilyunderstood with reference to FIGS. 26 and 27.

In general, at least one image sensor 353 can be spaced from an innerportion 336 of the ablation electrode 324 and within a volume at leastpartially defined by the ablation electrode 324 such that the at leastone image sensor 353 is directed toward the inner portion 336 of theablation electrode 324. As described in greater detail below, suchspacing of the at least one image sensor 353 relative to the innerportion 336 of the ablation electrode 324 can facilitate robustacquisition of images during a medical procedure. As also described ingreater detail below, such robust acquisition of images can be used toguide certain aspects of a medical procedure, including, for example,one or more of the following: detection of a first anatomical boundary(e.g., endocardium of a heart chamber); detection of tissue thickness;detecting shape; and providing feedback on lesion progress during RFablation.

Structural elements of the ablation electrode 324 can protect the atleast one image sensor 353 from forces encountered by the ablationelectrode 324 during delivery, deployment, use, or any combinationthereof. For example, the at least one image sensor 353 can be envelopedby the ablation electrode 324, with the ablation electrode 324protecting the at least one image sensor 353 from a plurality of axialand radial forces (e.g., as the ablation electrode 324 comes intocontact with tissue in an anatomic structure). Additionally, oralternatively, the structural elements of the ablation electrode 324 canfacilitate maintaining suitable spacing between the at least one imagesensor 353 and tissue such that the at least one image sensor 353 cancapture useful images of the tissue. As an example, a deformable portion342 of the ablation electrode 324 can be movable in a direction awayfrom the at least one image sensor 353 as the deformable portion 342expands from a compressed state to an uncompressed state (e.g., from adelivery configuration to a deployed configuration). Thus, continuingwith this example, the deformable portion 342 can be biased in adirection away from the at least one image sensor 353 to facilitatemaintaining spacing between the at least one image sensor 353 and tissuein contact with the deformable portion 342 of the ablation electrode324.

While the structural elements of the ablation electrode 324 canfacilitate protecting the at least one image sensor 353 and positioningthe at least one image sensor 353 relative to tissue, a plurality ofcells 347 defined by the structural elements of the ablation electrode324 can form an open area that facilitates imaging tissue beyond theablation electrode 324 (e.g., an open area that is greater than thetotal surface area of the inner portion 336 of the ablation electrode324). For example, with the open area formed by the plurality of cells347, the ablation electrode 324 can be at least partially transparent toimaging energy from the least one image sensor 353 such that theablation electrode 324 reflects less than half of imaging energydirected from the at least one image sensor 353 toward the ablationelectrode 324. That is, images formed by the at least one image sensor353 can show features of tissue beyond the ablation electrode 324 withlittle obstruction by the ablation electrode 324.

The at least one image sensor 353 can be positioned according to any ofvarious different imaging requirements associated with use of theablation electrode 324. Thus, for example, the at least one image sensor353 can be directed in a direction distal to the ablation electrode 324to facilitate imaging contact between the ablation electrode 324 andtissue along a plane substantially perpendicular to the shaft 322. Inmany instances, orientation of the at least one image sensor 353 in thisdirection can generally facilitate imaging a region of maximumapplication of force between the ablation electrode 324 and tissue incontact with the ablation electrode 324.

In certain instances, the at least one image sensor 353 can include atleast three image sensors. For example, the at least three image sensorscan be arranged relative to one another to provide improved spatialresolution, as compared to configurations including less than threeimage sensors. Continuing with this example, images of the at least oneimage sensor 353 can be combined to provide a physician with acontextual image of the position of the ablation electrode 324 in theanatomic structure.

In some implementations, the catheter 304 can further include anirrigation element 328 coupled to a distal end portion 332 of thecatheter shaft 322. The irrigation element 328 can be, for example, anyone or more of the irrigation elements described herein. Accordingly,irrigation fluid can be delivered from the irrigation element 328 towardthe inner portion 336 of the ablation electrode 324 to cool the ablationelectrode 324 according to any one or more of the various differentmethods described herein.

The at least one image sensor 353 can be disposed along the irrigationelement 328. It should be appreciated that positioning the at least oneimage sensor 353 on the irrigation element 328 can be useful for spacingthe at least one image sensor 353 away from the catheter shaft 322,which can be useful for providing a field of view that is substantiallyunobstructed by the catheter shaft 322. Additionally, or alternatively,positioning the at least one image sensor 353 on the irrigation element328 can facilitate achieving a field of view from a positionsubstantially in a middle portion of the ablation electrode 324.

The irrigation element 328 can define irrigation holes 334, with atleast a portion of the irrigation holes 334 directed toward a respectivefield of view of the at least one image sensor 353. For example, atleast a portion of the irrigation holes 334 can direct irrigation fluidbetween the irrigation element 328 and the inner portion of the ablationelectrode 336. In use, the direction of irrigation fluid toward therespective field of view of the at least one image sensor 353 canadvantageously displace blood from the field of view of the at least oneimage sensor 353 to facilitate the use of certain imaging modalities,such as the use of a camera as described in greater detail below. Thatis, the irrigation fluid (e.g., saline) can be substantially transparentto the at least one image sensor 353 such that the use of the irrigationfluid to displace blood from the field of view of the at least one imagesensor 353 can facilitate imaging tissue that would otherwise beobscured by blood moving between the at least one image sensor 353 andtissue to be imaged.

In general, the at least one image sensor 353 can include imagingmodalities suitable for detecting one or more parameters useful forguiding a medical procedure.

In certain implementations, the at least one image sensor 353 caninclude a camera such as, for example, a camera including a fish-eyelens. Additionally, or alternatively, the at least one image sensor 353can include a light source (e.g., a light emitting diode).

Through the use of irrigation fluid to displace blood from a field ofview of the camera (e.g., through delivery of irrigation fluid between afield of view of the camera and the inner portion 336 of the ablationelectrode 324), one or more images of tissue beyond the ablationelectrode 324 can be acquired. Such images can be useful, for example,for detecting contact between the ablation electrode 324 and a firstanatomic boundary and thus, in certain applications, can be useful forcreating a model of a blood-tissue boundary of the anatomic structure inwhich the ablation electrode 324 is disposed. Additionally, oralternatively, images acquired with a camera can be useful for providingfeedback regarding progression of a lesion being formed through theapplication of RF energy to tissue in the anatomic structure. Forexample, images acquired with a camera can be useful for detecting achange in wavelength or other parameter indicative of blanching oftissue as RF ablation energy is applied to the tissue. Further, orinstead, images acquired with a camera can be useful for identifying anyof various different anatomic landmarks (e.g., a valve) in the anatomicstructure.

In implementations in which the at least one image sensor 353 includes acamera, the camera can have a horizontal field of view and a verticalfield of view. At least one field of view of the camera can include atleast a distal half of the ablation electrode 324. For example, thecamera can have at least one field of view including an equator of thedeformable portion 342 in implementations in which the deformableportion 342 of the ablation electrode 324 is substantially spherical.Such an orientation of the field of view can be useful, for example, forproviding contextual information to the physician regarding the positionof the ablation electrode 324 within an anatomic structure. That is,orienting the field of view of a camera to include at least a distalhalf of the ablation electrode 324 can be useful for imaging tissue incontact with the ablation electrode 324 along primary directions ofmovement of the ablation electrode 324. Further, or instead, tofacilitate imaging tissue beyond the ablation electrode 324, a focallength of the at least one image sensor 353 can be outside of theablation electrode 324.

In some implementations, the at least one image sensor 353 can includeat least one ultrasound transducer. In such implementations, theablation electrode 324 disposed about the at least one ultrasoundtransducer can be useful for maintaining sufficient spacing between theultrasound transducer and tissue being imaged to facilitate acquiringuseful images of the tissue of the anatomic structure. In general, therecan be large variations in the response of an ultrasound transducer toreflections within the near field (or Fresnel region). Thus, as usedherein, “sufficient spacing” for an A-mode ultrasound transducer can beconsidered to include maintaining the tissue in the far field (orFraunhofer region) of the ultrasound transducer, beyond the Fresnelregion.

In general, the at least one ultrasound transducer can be in any number,shape, and arrangement, as required to achieve a suitable image. Thus,for example, the at least one ultrasound transducer can include a singleultrasound transducer. Continuing with this example, the singleultrasound transducer can be used in “A-mode” imaging, with the imagebeing a one-dimensional depth profile over time that can, optionally, bedisplayed on a graphical user interface. Additionally, or alternatively,two or more ultrasound transducers (e.g., six ultrasound transducers)can be arranged relative to one another to acquire images along multipledifferent dimensions of the anatomic structure. In certainimplementations, images acquired along multiple different dimensions canbe combined with one another (e.g., into a stereoscopic image) and shownon a graphical user interface (e.g., the graphical user interface 110 inFIG. 1). More generally, it should be appreciated that the term “image,”as used in the context of ultrasound transducers described herein,should be understood to include information detected by the at least oneultrasound transducer along one or more dimensions and, thus, isinclusive of the one-dimensional depth profile over time (acquired by asingle ultrasound transducer) as well as a combination of signals frommultiple ultrasound transducers.

For example, the at least one ultrasound transducer can be radiallysymmetric. Additionally, or alternatively, each ultrasound transducercan include an ultrasound transducer array of piezoelectric crystalsthat send ultrasound signals in a direction from the at least one imagesensor 353 toward the inner portion 336 of the ablation electrode 324 toimage tissue beyond the ablation electrode 324. Echoes of the ultrasoundsignals can be received at the array of piezoelectric crystals to forman ultrasound image, as is known in the art. In general, the at leastone image sensor 353 including the ultrasound transducer can provideinformation regarding tissue depth in an area being imaged.

In certain instances, the at least one image sensor 353 can include atleast one ultrasound transducer having a beam width at least twice aswide as a respective transverse dimension of at least some of struts 344b collectively defining a plurality of open cells 347. Through suchsizing, the struts 344 b can be at least partially transparent to theultrasound transducer beam and, therefore, the at least one image sensor353 can image tissue beyond the ablation electrode 324 with littleinterference from portions of the ablation electrode 324 between the atleast one ultrasound transducer and the tissue to be imaged. As anexample, the struts 344 b can be sized to reflect less than half of theultrasound energy of the ultrasound transducer beam directed from the atleast one image sensor 353 toward the ablation electrode 324.

The catheter 304 can further include a location sensor 330 fixedrelative to a distal end portion 332 of the catheter shaft 322. Thelocation sensor 330 can include, for example, a magnetic sensor such asany one or more of various magnetic position sensors well known in theart and that can be positioned at any point along the distal end portion332 of the catheter shaft 322. The location sensor 330 can, for example,include one or more coils that detect signals emanating from magneticfield generators. Continuing with this example, one or more coils fordetermining position with five or six degrees of freedom can be used. Amagnetic field detected by the location sensor 130 can be used todetermine the position of the distal end portion 332 of the cathetershaft 322 according to one or more methods commonly known in the artsuch as, for example, methods based on using the magnetic sensor tosense magnetic fields in the bed and using a look-up table to determinelocation of the location sensor 330.

Because the location sensor 330 is coupled to the distal end portion 332of the catheter shaft 322 in a known, fixed relationship to the at leastone image sensor 353, the location sensor 330 can provide locationinformation associated with images acquired by the at least one imagesensor 353. Such location information can be useful, for example, fordisplaying the images on a graphical user interface (e.g., the graphicaluser interface 110 in FIG. 1) along with a representation of theablation electrode 324, the anatomic structure, or both. Thus, as aspecific example, the physician can use a combination of images from theat least one image sensor 353 and a representation of the ablationelectrode 324 relative to a representation of an anatomic structure toposition the ablation electrode 324 along a desired location of theanatomic structure. Additionally, or alternatively, the locationinformation associated with the images can be useful for tagginglocations on a model of the anatomic structure based on one or morefeatures observed in the images shown on the graphical user interface.

Referring now to FIGS. 1 and 26-30, the catheter interface unit 108 canbe in communication with the at least one image sensor 353, and thegenerator 116 can be in electrical communication with the ablationelectrode 324. The storage medium 109 b can have stored thereon computerexecutable instructions for causing one or more processors of theprocessing unit 109 a to execute any one or more of various, differentexemplary methods including, for example, the exemplary methods shown inFIGS. 28-30.

Referring now to FIG. 28, an exemplary method 2800 can include receiving2802 at least one image from at least one image sensor, generating 2804a graphical representation of an anatomic structure based on the atleast one image, and sending 2806 the graphical representation of theanatomic structure to a graphical user interface. In general, any one ormore of the steps of the exemplary method 2800 can be implemented usingany one or more of the devices, systems, and methods described herein,unless otherwise indicated or made clear from the context.

In general, the at least one image from the at least one image sensorcan be received 2802 at a catheter interface unit (e.g., the catheterinterface unit 108 in FIG. 1) through wired communication, wirelesscommunication, or a combination thereof. In certain implementations, theat least one image from the at least one image sensor can be received2802 periodically (e.g., at a substantially fixed frequency). Forexample, the at least one image from the image sensor can be received2802 at a frequency (e.g., at least about 10 images per second)sufficient to form a substantially continuous display of the images on agraphical user interface. In some implementations, however, the at leastone image from the at least one image sensor can be received 2802intermittently, such as at predetermined intervals, in response to acommand from a physician, during periods in which irrigation fluid isdelivered to displace blood from a field of view, during periods ofdetected contact with tissue, and combinations thereof.

Generating 2804 the graphical representation of the anatomic structurebased on the at least one image can include, for example, combininginformation from a plurality of images of the anatomic structure as theablation electrode is moved through the anatomic structure. For example,in implementations in which the at least one image sensor includes anultrasound transducer, combining information from a plurality of imagescan be useful for reducing noise and, further or instead, for moreclearly resolving structures. More generally, reflected imaging energycan vary significantly with angle and, thus, it can be useful to imagethe same location from multiple views and combine such information togenerate 2804 the graphical representation of the anatomic structure.

At least some of the images of the plurality of images can correspond todifferent locations of the ablation electrode in the anatomic structure.Additionally, or alternatively, the graphical representation can bebased at least in part on the known location of the ablation electrodecorresponding to the respective image. The known location of theablation electrode can be based on any one or more of the methodsdescribed herein. Thus, for example, the location of the ablationelectrode in the anatomic structure can be based at least in part on anelectric field present in at least a portion of the anatomic structure.Additionally, or alternatively, the location of the ablation electrodein the anatomic structure can be based at least in part on a signal froma magnetic sensor fixed relative to a distal end portion of a cathetershaft carrying the ablation electrode.

In certain implementations, generating 2804 the graphical representationof the anatomic structure can include detecting an anatomical boundarybased at least in part on the at least one image. As an example, becausethe position of the at least one image sensor is known (e.g., through asubstantially fixed relationship to the location sensor) as the ablationelectrode is moved through the anatomic structure, the detection of theanatomical boundary in multiple images can be combined to form thegraphical representation. As a more specific example, the anatomicboundary can include a blood-tissue boundary and, in certain instances,one or more of the position and shape of the blood-tissue boundary canbe based on the at least one image. In some implementations, theposition and shape of the blood-tissue boundary determined based on theat least one image can be further based on signals indicative of contactbetween the ablation electrode and tissue.

Detecting the anatomical boundary can be achieved through analysis ofthe at least one image. Such analysis can include, for example,application of machine vision to the at least one image. Additionally,or alternatively, detecting the anatomical boundary can be based on aninput from a physician or technician (e.g., a tag indicative of ananatomic landmark such as a valve).

Generating 2804 the graphical representation of the anatomic structurecan, further or instead, include detecting a shape of the anatomicboundary based at least in part on the at least one image. For example,the at least one image can be used to determine the shape of thedeformable portion of the ablation electrode as the deformable portioncontacts tissue. That is, the shape of the deformable portion of theelectrode can change based on the amount and direction of force ofcontact between the anatomic structure and the deformable portion of theelectrode (e.g., according to any one or more of the implementationsdescribed herein, unless otherwise specified or made clear from thecontext). Thus, the shape of the deformable portion detected in theimage can be used to determine one or more of force of contact anddirection of contact. Such information regarding direction and force ofcontact can be useful for, among other things, positioning thedeformable portion of the ablation electrode for the delivery of energyto the tissue. Additionally, or alternatively, information regardingdirection and force of contact can be useful for providing local shapeinformation regarding the area of contact between the anatomic structureand the deformable portion of the ablation electrode, with such localshape information useful, for example, for forming an accuraterepresentation of the anatomic structure on the graphical userinterface.

In implementations in which the at least one image is an ultrasoundimage or another type of image suitable for detecting thickness oftissue, generating 2804 the graphical representation of the anatomicstructure can include determining thickness of the tissue of theanatomic structure based at least in part on the at least one image. Asused herein, thickness of tissue of the anatomic structure generallyincludes a distance from one surface of tissue to another surface oftissue and, more specifically, can include a distance from one surfaceof tissue to another surface of tissue along an axis perpendicular to atleast one of the surfaces of tissue.

In implementations in which the anatomic structure is a cavity of theheart, for example, thickness of the tissue should be understood toinclude a distance between endocardial tissue and epicardial tissue. Inparticular, cardiac muscle has characteristics that can be useful formeasuring thickness of tissue using ultrasound. That is, as compared toblood and other fluids (e.g., irrigation fluid) present in the heartduring a cardiac procedure, cardiac muscle is generally both morereflective and more attenuative to ultrasound. Thus, the endocardialboundary of the cardiac muscle can be readily detected as an increase inreflected energy in response to ultrasound energy. The epicardialboundary can be detected as a change in reflection (e.g., a narrowreduction, step change, or both). Further, or instead, the epicaridalboundary can be detected as a difference in velocity (e.g., a Dopplerdetection method). Accordingly, it should be understood that thethickness of the tissue of the cavity of the heart can be determined asa difference in distance between these boundaries. In certain instances,the thickness of the heart cavity can be determined along variousdifferent directions along the heart cavity as ultrasound images areacquired at various different locations, and the thickness of the heartcavity can be determined at various different locations along thetissue. While the determination of thickness has been described as beinguseful for a heart cavity, it should be appreciated that such thicknessdetermination can, more generally, be useful in any anatomic structurein which surfaces separated by tissue are detectable through the use ofultrasound.

Determination of thickness can be useful for, among other uses,providing feedback regarding the amount of ablation power suitable forforming a lesion at a given location of the anatomic structure. Thefeedback provided regarding thickness of the anatomic structure caninclude, as an example, a display of visual indicia of the thickness onthe graphical user interface. The visual indicia of the thickness cantake any one or more of various forms, including a thickness map of theanatomic structure, with the map showing variation of thickness atvarious different positions along the anatomic structure. The variationof thickness in the map can be based on, for example, a color scale suchthat differences in thickness can be readily appreciated by a physician,or other personnel, using the map as part of a medical procedure. Incertain implementations, the thickness map of the anatomic structure canbe sliced along any one or more of various different planes to show across-section of tissue thickness at a given point along the anatomicstructure. For example, a physician, or other personnel, can select aplane useful for visualization of tissue thickness along a particularportion of the anatomic structure, and the thickness map of the anatomicstructure can be sliced along the selected plane.

In certain implementations, generating 2804 the graphical representationcan include detecting progress of the lesion based on the at least oneimage. For example, in implementations in which the at least one imagesensor includes a camera, detecting progress of the lesion can includedetecting a change in color of tissue in the anatomic structure. Thechange in color can be, for example, indicative of progress of a lesionformed through the application of RF ablation energy from the ablationelectrode to the tissue. That is, the change in color can be a changefrom red to white as the tissue is ablated. Additionally, oralternatively, in implementations in which the at least one image sensorincludes an ultrasound transducer, detecting progress of the lesion caninclude detecting microbubbles formed as tissue is ablated anddetermining progress of the lesion based on the detected microbubbles.

An indication of the lesion progress can be sent to the graphical userinterface. For example, the indication of lesion progress can be shownon the graphical user interface to provide the physician with a visualrepresentation of progress of a lesion. Such visualization can beuseful, for example, for facilitating accurate application of lesions(e.g., an overlapping pattern) as part of a medical procedure.

Displaying 2806 the graphical representation of the anatomic structureon the graphical user interface can include any manner and form ofdisplay known in the art. Thus, for example, displaying 2806 thegraphical representation of the anatomic structure on the graphical userinterface can include projecting a two-dimensional representation of athree-dimensional model of the anatomic structure to a two-dimensionalgraphical user interface, such as a two-dimensional computer monitorwell known in the art. Additionally, or alternatively, displaying 2806the graphical representation of the anatomic structure on the graphicaluser interface can include displaying a three-dimensional model of theanatomic structure to a three-dimensional display, such as a virtualreality or an augmented reality display environment.

Referring now to FIG. 29, an exemplary method 2900 can include receiving2902 at least one image from at least one image sensor, and determining2904 tissue thickness based on the at least one image. In general, anyone or more of the steps of the exemplary method 2900 can be implementedusing any one or more of the devices, systems, and methods describedherein, unless otherwise indicated or made clear from the context.

Receiving 2902 the at least one image from the at least one image sensorcan include any one or more of the various different methods ofreceiving an image described herein. Thus, for example, receiving 2902the at least one image from the at least one image sensor should beunderstood to be similar to the step of receiving 2802 the at least oneimage described with respect to the exemplary method 2800 (FIG. 28),unless otherwise indicated or made clear from the context.

Determining 2904 thickness of tissue of the anatomic structure caninclude any one or more of the various different methods of determiningthickness described above with respect to the exemplary method 2800(FIG. 28), unless otherwise indicated or made clear from the context.Likewise, any of the various different methods of determining 2904described with respect to the exemplary method 2900 should be understoodto be interchangeable with implementations of the exemplary method 2800including tissue thickness determination, unless otherwise indicated ormade clear from the context.

In certain implementations, the determining 2904 thickness of tissue ofthe anatomic structure can be based on a three-dimensional localizationof the at least one image sensor. The three-dimensional localization canbe based, for example, on one or more location signals received from alocation sensor carried by the catheter and, more specifically, can bebased on signals received from any one or more of the location sensorsdescribed herein.

In general, respiration, heartbeat, and movement of blood past andthrough the ablation electrode can cause small, unintentional movementsof the at least one image sensor during use. Accordingly, in someimplementations, signal processing of the at least one image and/orgating based on heartbeat or respiration can be useful for makingdeterminations based on the at least one image. For example, determining2904 thickness of tissue of the anatomic structure can be based oninformation from one or more previous positions of the at least oneimage sensor to smooth the influence of fluctuation of position of theat least one image sensor. More specifically, the smoothing can be basedon previously received images, previously received locations, or acombination thereof. It should be understood that smoothing thedetermined 2904 tissue thickness can reduce the influence of any oneimage or position on the overall tissue thickness map and, thus, can beuseful for improving overall accuracy of a tissue thickness map of theanatomic structure.

Referring now to FIG. 30, an exemplary method 3000 of using at least oneimage sensor can include expanding 3002 an ablation electrode from acompressed state to an uncompressed state, positioning 3004 an outerportion of the ablation electrode at a treatment site, acquiring 3006 atleast one image of the treatment site from at least one image sensor,and delivering 3008 RF energy to the ablation electrode at the treatmentsite based at least in part on the at least one image of the treatmentsite. In general, the exemplary method 3000 can be carried out using anyone or more of the devices, systems, and methods described herein,unless otherwise indicated or made clear from the context.

Expanding 3002 the ablation electrode from the compressed state to theuncompressed state can include any one or more of the various differentdevices, systems, and methods of expanding an ablation electrodedescribed herein. In general, the ablation electrode can include aplurality of struts (e.g., the struts 344 b shown in FIGS. 26 and 27)defining a plurality of cells (e.g., the cells 347 shown in FIGS. 26 and27). The struts can flex away from one another to expand 3002 theablation electrode from the compressed state to the uncompressed state.The at least one image sensor can be proximal to an inner portion of theablation electrode such that the ablation electrode in the uncompressedstate envelops the at least one image sensor. In certainimplementations, expanding 3002 the ablation electrode includes movingthe ablation electrode in a direction away from the at least one imagesensor. Blood can move between the at least one image sensor and theinner portion of the ablation electrode with the ablation electrode inthe uncompressed state.

Positioning 3004 the ablation electrode at the treatment site caninclude, for example, moving the ablation electrode into contact withtissue. Such movement of the ablation electrode can be guided, forexample, by one or more images acquired 3006 from the at least one imagesensor. For example, the one or more images acquired 3006 by from the atleast one image sensor can detect an anatomic boundary according to anyone or more of the methods described herein, and positioning 3004 theablation electrode can be based on a representation of the detectedanatomic boundary on a graphical user interface. As a specific example,the graphical representation of the anatomic boundary can include arepresentation of endocardial tissue of a patient's heart.

Acquiring 3006 the at least one image of the treatment site from atleast one image sensor can include acquiring a plurality of images ofthe treatment site from respective different locations of the ablationelectrode within the anatomic structure according to any one or more ofthe various different devices, systems, and methods described herein.Thus, for example, acquiring 3006 the at least one image of thetreatment site from the at least one image sensor can include receivingone or more of an image from a camera, an ultrasound transducer, or acombination thereof, as the ablation electrode is moved in the anatomicstructure.

Further, or instead, acquiring 3006 the at least one image of thetreatment site can include determining a location associated with eachrespective image and forming a graphical representation of an anatomicboundary based on the plurality of images and the associated locations,also according to any one or more of the various different devices,systems, and methods described herein. Thus, for example, determiningthe location associated with each respective image can be based on anelectric field present in at least a portion of the anatomic structure.The electric field can be at least partially generated by one or moreelectrodes external to the anatomic structure (e.g., a return electrode,such as the return electrode 118 in FIG. 1). Further, or instead, theelectric field can be at least partially generated by one or moreelectrodes carried by the catheter within the anatomic structure, suchas any of the various sensors described herein (e.g., the sensors 126 inFIGS. 3 and 4).

Delivering 3008 RF energy to the ablation electrode at the treatmentsite based at least in part on the at least one image of the treatmentsite can include, for example, varying RF energy delivery based ontissue thickness at the treatment site. The tissue thickness can bedetermined, for example, according to any one or more of the variousdifferent methods described herein and, thus, can be based on one ormore ultrasound images acquired by the one or more image sensors.

The above systems, devices, methods, processes, and the like may berealized in hardware, software, or any combination of these suitable fora particular application. The hardware may include a general-purposecomputer and/or dedicated computing device. This includes realization inone or more microprocessors, microcontrollers, embeddedmicrocontrollers, programmable digital signal processors or otherprogrammable devices or processing circuitry, along with internal and/orexternal memory. This may also, or instead, include one or moreapplication specific integrated circuits, programmable gate arrays,programmable array logic components, or any other device or devices thatmay be configured to process electronic signals.

It will further be appreciated that a realization of the processes ordevices described above may include computer-executable code createdusing a structured programming language such as C, an object orientedprogramming language such as C++, or any other high-level or low levelprogramming language (including assembly languages, hardware descriptionlanguages, and database programming languages and technologies) that maybe stored, compiled or interpreted to run on one of the above devices,as well as heterogeneous combinations of processors, processorarchitectures, or combinations of different hardware and software. Inanother aspect, the methods may be embodied in systems that perform thesteps thereof, and may be distributed across devices in a number ofways. At the same time, processing may be distributed across devicessuch as the various systems described above, or all of the functionalitymay be integrated into a dedicated, standalone device or other hardware.In another aspect, means for performing the steps associated with theprocesses described above may include any of the hardware and/orsoftware described above. All such permutations and combinations areintended to fall within the scope of the present disclosure.

Embodiments disclosed herein may include computer program productscomprising computer-executable code or computer-usable code that, whenexecuting on one or more computing devices, performs any and/or all ofthe steps thereof. The code may be stored in a non-transitory fashion ina computer memory, which may be a memory from which the program executes(such as random access memory associated with a processor), or a storagedevice such as a disk drive, flash memory or any other optical,electromagnetic, magnetic, infrared or other device or combination ofdevices.

In another aspect, any of the systems and methods described above may beembodied in any suitable transmission or propagation medium carryingcomputer-executable code and/or any inputs or outputs from same.

The method steps of the implementations described herein are intended toinclude any suitable method of causing such method steps to beperformed, consistent with the patentability of the following claims,unless a different meaning is expressly provided or otherwise clear fromthe context. So, for example performing the step of X includes anysuitable method for causing another party such as a remote user, aremote processing resource (e.g., a server or cloud computer) or amachine to perform the step of X. Similarly, performing steps X, Y and Zmay include any method of directing or controlling any combination ofsuch other individuals or resources to perform steps X, Y and Z toobtain the benefit of such steps. Thus, method steps of theimplementations described herein are intended to include any suitablemethod of causing one or more other parties or entities to perform thesteps, consistent with the patentability of the following claims, unlessa different meaning is expressly provided or otherwise clear from thecontext. Such parties or entities need not be under the direction orcontrol of any other party or entity, and need not be located within aparticular jurisdiction.

It should further be appreciated that the methods above are provided byway of example. Absent an explicit indication to the contrary, thedisclosed steps may be modified, supplemented, omitted, and/orre-ordered without departing from the scope of this disclosure.

It will be appreciated that the methods and systems described above areset forth by way of example and not of limitation. Numerous variations,additions, omissions, and other modifications will be apparent to one ofordinary skill in the art. In addition, the order or presentation ofmethod steps in the description and drawings above is not intended torequire this order of performing the recited steps unless a particularorder is expressly required or otherwise clear from the context. Thus,while particular embodiments have been shown and described, it will beapparent to those skilled in the art that various changes andmodifications in form and details may be made therein without departingfrom the spirit and scope of this disclosure and are intended to form apart of the invention as defined by the following claims, which are tobe interpreted in the broadest sense allowable by law.

What is claimed is:
 1. A catheter comprising: a catheter shaft having aproximal end portion and a distal end portion; an ablation electrodecoupled to the distal end portion of the catheter shaft, the ablationelectrode having an inner portion and an outer portion opposite theinner portion; and at least one image sensor spaced from the innerportion of the ablation electrode and disposed within a volume at leastpartially defined by the ablation electrode, the at least one imagesensor directed toward the inner portion of the ablation electrode. 2.The catheter of claim 1, wherein the ablation electrode includes adeformable portion movable in a direction away from the at least oneimage sensor as the deformable portion expands from a compressed stateto an uncompressed state.
 3. The catheter of claim 1, wherein the atleast one image sensor is enveloped by the ablation electrode.
 4. Thecatheter of claim 3, wherein the ablation electrode is at leastpartially transparent to imaging energy from the at least one imagesensor such that the ablation electrode reflects less than half of theimaging energy directed from the at least one image sensor toward theablation electrode.
 5. The catheter of claim 3, wherein the ablationelectrode defines an open area greater than the total surface area ofthe inner portion of the ablation electrode.
 6. The catheter of claim 1,further comprising an irrigation element coupled to the distal endportion of the catheter shaft.
 7. The catheter of claim 6, wherein theat least one image sensor is disposed along the irrigation element. 8.The catheter of claim 6, wherein the irrigation element definesirrigation holes directed toward a respective field of view of the atleast one image sensor.
 9. The catheter of claim 8, wherein theirrigation holes defined by the irrigation element are directed towardthe respective field of view of the at least one image sensor betweenthe irrigation element and the inner portion of the ablation electrode.10. The catheter of claim 1, wherein the at least one image sensorincludes a camera.
 11. The catheter of claim 1, wherein the at least oneimage sensor includes at least one ultrasound transducer.
 12. A methodcomprising: expanding an ablation electrode from a compressed state toan uncompressed state, an inner portion of the ablation electrode in theuncompressed state enveloping at least one image sensor; positioning anouter portion of the ablation electrode at a treatment site in ananatomic structure, the outer portion of the ablation electrode oppositethe inner portion of the ablation electrode; acquiring at least oneimage of the treatment site from the at least one image sensor; anddelivering RF energy to the ablation electrode at the treatment sitebased at least in part on the at least one image of the treatment site.13. The method of claim 12, wherein expanding the ablation electrodefrom the compressed state to the uncompressed state includes moving theablation electrode in a direction away from the at least one imagesensor.
 14. The method of claim 12, wherein blood is movable between theat least one image sensor and the inner portion of the ablationelectrode with the ablation electrode in the uncompressed state.
 15. Themethod of claim 12, further comprising determining tissue thickness atthe treatment site based at least in part on the at least one image. 16.The method of claim 15, wherein delivering RF energy to the ablationelectrode is based on the tissue thickness at the treatment site. 17.The method of claim 12, further comprising detecting an anatomicboundary based on the at least one image of the treatment site.
 18. Themethod of claim 17, wherein positioning the outer portion of theablation electrode at the treatment site is based at least in part onthe detected anatomic boundary.
 19. The method of claim 12, wherein theat least one image sensor includes at least one camera and acquiring theimage of the treatment site from the at least one image sensor includesdelivering irrigation fluid to a respective field of view of the leastone camera.
 20. The method of claim 19, wherein the at least one imagesensor is spaced from the inner portion of the ablation electrode by adistance less than a focal length of the at least one image sensor. 21.The method of claim 19, wherein the irrigation fluid is deliveredbetween the at least one camera and the inner portion of the ablationelectrode.
 22. The method of claim 12, wherein the at least one imagesensor includes at least one ultrasound transducer.
 23. The method ofclaim 22, wherein the at least one image sensor is spaced from the innerportion of the ablation electrode by a distance greater than a focallength of the at least one image sensor.
 24. The method of claim 12,wherein delivering RF energy to the ablation electrode is based ondetection of microbubbles detected by the at least one image sensor.